U.S. patent number 4,399,241 [Application Number 06/132,507] was granted by the patent office on 1983-08-16 for base for a graft polymer, novel graft polymer compositions, solvents and water-reducible coatings incorporating the novel graft polymers, and processes for making them.
This patent grant is currently assigned to SCM Corporation. Invention is credited to Richard M. Marcinko, Vincent W. Ting, James T. K. Woo.
United States Patent |
4,399,241 |
Ting , et al. |
August 16, 1983 |
Base for a graft polymer, novel graft polymer compositions,
solvents and water-reducible coatings incorporating the novel graft
polymers, and processes for making them
Abstract
Provides new and improved water-reducible coating compositions
and methods of making them. Three preferred processes are
disclosed. These differ in the manner of incorporating and chemical
nature of an extender polymer. Broadly, the process of the
invention is one for forming an aqueous dispersion of a fluent
resinous composition of a. a mixture in an organic solvent of (i)
an ionizable graft polymer of an epoxy resin and an addition
polymerized resin, the addition polymerized resin being bonded to
aliphatic backbone carbon atoms of the epoxy resin by
carbon-to-carbon bonds, and (ii) an extender resin; b. an aqueous
vehicle, and c. an ionizing agent; the ionization present from said
combined components being sufficient to establish the components as
a dispersion in the aqueous vehicle, and then addition polymerizing
a quantity of addition polymerizable monomer, under addition
polymerizing conditions, in said aqueous dispersion, the aqueous
dispersion serving as a vehicle therefor. In another aspect of the
invention, a grafting base is produced by advancing an aromatic
epoxy resin in the presence of at least one extender resin and a
sufficient amount of an organic solvent to render the initial
mixture and grafting base product fluent.
Inventors: |
Ting; Vincent W. (Boulder,
CO), Woo; James T. K. (Medina, OH), Marcinko; Richard
M. (North Royalton, OH) |
Assignee: |
SCM Corporation (New York,
NY)
|
Family
ID: |
22454361 |
Appl.
No.: |
06/132,507 |
Filed: |
March 21, 1980 |
Current U.S.
Class: |
523/400; 523/427;
523/434; 525/107; 525/108; 525/111; 525/112; 525/120; 525/122;
525/416; 525/438; 525/454; 525/529; 525/531; 525/63 |
Current CPC
Class: |
C08F
283/10 (20130101); C09D 151/00 (20130101); C09D
151/00 (20130101); C08L 2666/28 (20130101) |
Current International
Class: |
C08F
283/10 (20060101); C08F 283/00 (20060101); C09D
151/00 (20060101); C08L 063/02 () |
Field of
Search: |
;525/122,416,108,63,107,111,112,120,438,454,529,531 ;528/106
;523/400,427,434 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Pertilla; Theodore E.
Attorney, Agent or Firm: Schmitz; Thomas M.
Claims
What is claimed is:
1. A process for making a fluent blend of an advanced epoxy resin
and an extender polymer, said epoxy resin and said extender polymer
each having aliphatic backbone carbon atoms that have either one or
two carbon atoms bonded thereto, which comprises:
mixing an aromatic 1,2-epoxy resin, having an epoxy equivalent
weight below about 2,000, with at least one extender polymer and
with a sufficient amount of an organic solvent to render the
mixture fluent, and then
advancing the epoxy resin in the presence of said extender polymer
and said solvent, by reacting the epoxy resin with a polyfunctional
compound that adds to the epoxy resin at its epoxide groups, to
increase the molecular weight of the resin, which polyfunctional
compound is either a polycarboxylic compound or a polyhydroxy
compound,
maintaining sufficient solvent in the mixture that the blend of
advanced epoxy resin and extender polymer remains fluent, and
polymerizing addition polymerizable monomer in the presence of said
mixture by addition polymerization under addition polymerizing
conditions.
2. The process of claim 1 wherein the epoxy resin is an adduct of a
diglycidyl ether of a bisphenol that has an epoxy equivalent weight
in the range from about 180 up to about 2,000, and the resin is
advanced by reacting it at a temperature in the range from about
130.degree. C. to about 250.degree. C. with a bisphenol, to the
point that it has an epoxy equivalent weight above about 2,000.
3. The process of claim 2 wherein the extender polymer is a
hydrocarbon polymer.
4. The process of claim 2 wherein the extender polymer is selected
from the group consisting of a low molecular weight polyethylene,
polystyrene, a styrene acrylate copolymer, an ethylene-vinyl
acetate copolymer, a hydroxyl-terminated polyester or polyurethane,
a styrene-acrylonitrile copolymer, a hydrocarbon resin, an epoxy
resin, and mixtures of two or more of these.
5. The process of claim 2 wherein the extender polymer is
ethylenically unsaturated and addition polymerizable.
6. The process of claim 5 wherein the extender polymer is a
polybutadiene.
7. The process of claim 2 wherein the extender polymer is a
different epoxy resin than said first-named, aromatic, 1,2-epoxy
resin.
8. The process of claim 7 wherein the extender polymer is
epoxidized polybutadiene.
9. The process of claim 1 wherein the polyfunctional compound is
one that reacts with the epoxy resin to extend the resin and to
increase the number of aliphatic backbone carbon atoms that have
either one or two carbons bonded thereto.
10. The process of claim 9 wherein the polyfunctional compound is
an aromatic polyhydric alcohol.
11. The process of claim 10 wherein the polyfunctional compound is
a diphenol.
12. The process of claim 11 wherein the polyfunctional compound is
bisphenol A.
13. The process of claim 1 or 2 wherein the polyfunctional compound
is a polynuclear polyhydroxy phenol.
14. The process of claim 2 wherein the bisphenol is bisphenol A and
the extender polymer is polystyrene.
15. A process according to claim 1 wherein the polyfunctional
compound is a polycarboxylic acid or a polycarboxylic acid
anhydride.
16. The process of claim 15 wherein the polyfunctional compound is
a saturated aliphatic polycarboxylic acid or polycarboxylic acid
anhydride.
17. The process of claim 15 wherein the polyfunctional compound is
adipic acid.
18. The process of claim 15 wherein the acid is azelaic acid.
19. The process of claim 15 wherein the polyfunctional compound is
a cyclic polycarboxylic acid or a cyclic polycarboxylic acid
anhydride.
20. The process of claim 19 wherein the polyfunctional compound is
a tetrahydrophthalic acid or anhydride.
21. The process of claim 19 wherein the polyfunctional compound is
a phthalic acid or anhydride.
22. The process of claim 2 wherein the solvent employed is one that
dissolves the blend.
23. The process of claim 2 wherein the solvent employed comprises
2-butoxyethanol-1.
24. The process of claim 23 wherein the solvent also comprises
n-butanol.
25. The process of claim 2, 3, 11, or 22, wherein the epoxy resin
has a molecular weight, following advancement, of not substantially
less than 4,000, and forms at least 50% by weight of the blend
following advancement.
26. A tractable blend produced by the process of claim 1, 2, 3, 11,
22, 23 or 24.
27. A process for producing a fluent resinous composition which
comprises:
forming a tractable blend substantially free from particulate
resinous matter, said blend consisting essentially of polyepoxy
resin, extender polymer and organic solvent;
advancing at a temperature between about 130.degree. C. and
250.degree. C. said polyepoxy resin in said blend to greater
molecular weight by reacting said polyepoxy resin with epoxy resin
advancing agent,
said extender polymer and said solvent being inert towards said
polyepoxy resin and said advancing agent under the blend forming
and advancing conditions used and, effecting termination of the
advancement while the resulting mass remains tractable,
polymerizing addition polymerizable monomer in the presence of said
resulting mass by addition polymerization under addition
polymerizing conditions.
28. The process of claim 27 wherein the advanced epoxy resin
retains some oxirane functionality.
29. The process of claim 28 wherein at least part of the remaining
oxirane functionality is modified by reaction with oxirane
modifying agent that is monofunctional with respect to reacting
with oxirane groups, thereby forming a modified mass.
30. The process of claim 29 wherein said reaction with said
modifying agent provides the modified mass with ionizable
functionality.
Description
RELATED PATENT APPLICATIONS
The subject matter of the present patent application is related to
the subjects matter of several other patent applications, the
teachings of which, particularly as identified below, are all
incorporated herein by reference.
The earliest-filed application on related technology is Ser. No.
685,246, filed May 11, 1976, and now abandoned.
Another patent application on related subject matter is Ser. No.
788,611, filed Apr. 18, 1977, which was a continuation-in-part of
the first-filed patent application, and which has been published as
Belgian Pat. No. 854,476, granted Nov. 10, 1977, and as German OS
No. 2,721,822, published Nov. 24, 1977.
A third application on related subject matter is Ser. No. 788,454,
filed Apr. 18, 1977, and now abandoned, which was also a
continuation-in-part of the first-filed patent application. This
third patent application was abandoned in favor of Ser. No.
793,507, filed May 4, 1977, which is published as Belgian Pat. No.
854,523, granted Nov. 14, 1977; as German No. OS 2,721,823.1; and
as Dutch Patent Application No. 77.05236, published Nov. 11,
1977.
U.S. Application Ser. No. 793,507 is a continuation-in-part of Ser.
No. 788,454. It was abandoned in favor of a continuation
application, Ser. No. 038,547, filed May 14, 1979.
A fifth patent application on related subject matter is Ser. No.
29,106, filed Apr. 11, 1979.
FIELD OF THE INVENTION
This invention relates to a process for making a fluent, filterable
blended material containing an epoxy resin and a second, extender
polymer, both of which have aliphatic backbone carbon atoms at
which grafting can take place, and processes for making such
blends.
The invention is also concerned with the processes for making novel
graft polymer compositions from these blends, and to coating
compositions utilizing these novel graft polymer compositions, and
to the products thus obtained.
In a particular and preferred embodiment, the invention is
concerned with sprayable, water-reducible coating compositions
suitable for application to the interior of metal containers, such
as cans, useful for packaging beverages.
BACKGROUND OF THE PRESENT INVENTION
There is a continuing demand for improved types of coating
compositions, both solvent-based and water-reducible. More
specifically, there is a continuing and growing demand for
water-reducible, sprayable compositions suitable for application to
metal surfaces intended to come in contact with beverages, and
especially, for lining the interior of beverage cans.
Of the patent applications identified above, Ser. Nos. 685,246,
788,611 and 793,507 describe novel, sprayable, water-reducible
coating compositions that are particularly useful for lining
beverage cans. The compositions described have superior
metal-coating characteristics derived from an epoxy resin
component, and economy contributed by a vinyl resin component.
These important characteristics are available, moreover, in
compositions that when cured meet the many demanding tests with
which any beverage can lining composition is confronted.
Nevertheless, the need for continuing improvement in functional
characteristics, in economy, and in properties that facilitate
compliance with environmental protection legislation, particularly
with respect to the release of solvents to the atmosphere, indicate
the need for still further technological change and progress.
The first-filed application above, Ser. No. 685,246, in one
preferred embodiment, discloses a process for preparing a curable
resinous composition having an Acid Number of at least 30, by
reacting together at 90.degree. C. to 130.degree. C. an aromatic
1,2-epoxy diepoxide resin having a molecular weight above 350 and
addition polymerizable monomer of which from 10% to 80% by weight
is an acrylic acid, the diepoxide resin being present in sufficient
quantity to provide from 10% to 90% by weight of the initial
reaction mixture, in the presence of a free radical initiator of
the benzoyl peroxide type. During the reaction there is
simultaneous addition polymerization of the monomer through its
ethylenic unsaturation and grafting of addition polymer to the
epoxy resin. The graft polymer is characterized by the substantial
absence of hydrolyzable functional groups. The ionizability of the
reaction mixture, by reason of its acid functionality, is
sufficiently high to effect stable dispersion of the product in an
aqueous ionizing medium.
In a preferred embodiment, an aromatic diepoxide such as a
polyglycidyl ether of bisphenol A is reacted with a mixture of
addition polymerizable monomers containing a major amount of
methacrylic acid. The epoxy resin has a molecular weight of at
least 1,000, and provides from 30% to 90% of the initial reaction
mixture. The reaction takes place in the presence of benzoyl
peroxide at a temperature of 90.degree. C. to 130.degree. C., to
effect addition polymerization of the monomer and to produce a
graft polymer of addition polymer to the diepoxide having an Acid
Number of 30 to 150 or more, preferably 70-90. The reaction product
may be dispersed in a basic aqueous medium, to form a
water-reducible coating composition. Generally a cross-linker is
added, such as an aminoplast, and curing is effected in an oven.
Most preferably the epoxy resin has a molecular weight in the range
4,000 to 10,000 and provides 50% to 90% of the initial reaction
mixture.
As is more particularly pointed out in patent application Ser. No.
788,611, the resinous reaction product produced contains three
polymeric components, namely, the graft polymer, ungrafted epoxy
resin, and ungrafted addition polymer.
As is pointed out in Ser. No. 793,507, the initial epoxy resin,
that is employed in the graft polymer production process, may be
terminated to eliminate part or all of the terminal epoxy groups,
to eliminate ester grafting at the terminal epoxy groups.
Elimination of the terminal epoxy groups also permits the efficient
use of a wider variety of peroxide-type free radical initiators,
over a broader reaction temperature range, than would otherwise be
the case.
As is disclosed in these prior applications, in order to make
acceptable water-reducible coating compositions, the addition
polymerizable monomer comprises a major proportion of an
unsaturated carboxylic acid, preferably either acrylic or
methacrylic acid. Sufficient acid is employed so that the Acid
Number (NV, i.e., based on non-volatiles) of the reaction product
is from about 30 to 200. The ionizability of compositions prepared
in accordance with these several patent applications is based on
the acid functionality of the graft polymer and of the ungrafted
addition polymer. When the carboxyl groups are ionized by the
addition of such a composition to an aqueous vehicle containing an
amine or other fugitive base, an aqueous dispersion is produced
that is water-reducible. Such dispersions are stable over long
storage periods even at somewhat elevated temperatures, and remain
free from gelatin and precipitation. Only slight changes occur in
pH levels and viscosities, indicating very little change in
composition.
The reaction products of these prior applications appear to have
remarkable properties. Their contents of ionized polymers are
believed to serve as the means by which the ungrafted, nonionized
epoxy resin component is kept in stable suspension.
For sanitary coating applications of the prior applications, Ser.
Nos. 788,611 and 793,507, the preferred compositions are obtained
from initial reaction mixtures in which the solids are derived 50%
or more by weight from an epoxy resin having a molecular weight of
at least 4,000, and the balance from addition polymerizable monomer
of which the major proportion is acrylic or methacrylic acid. In a
more preferred embodiment of such a sprayable sanitary coating
composition, the solids of the reaction mixture are derived from an
epoxy resin that contributes from 60% to 90%, and preferably about
80%, by weight of the solids, the balance being a monomer mixture
of methacrylic acid, styrene, and ethyl acrylate, where the acid is
the predominant monomer. Preferred sanitary coating compositions
produced from such reaction mixtures have Acid Numbers (N.V.) in
the range from about 80 to about 90 and preferably about 85.
While resinous coating compositions of these kinds have excellent
functional characteristics and other highly desirable properties,
the high content of epoxy resin increases the cost. It would
therefore be highly desirable to find some way to produce
functionally equivalent materials, at lower cost.
Still another important consideration is the release of solvent
materials into the atmosphere. In the process of making the
reaction products of the patent applications described above, it
has been customary to use liquid organic solvent to facilitate
handling during the manufacturing process and to improve
application properties.
In the most preferred embodiment of the invention, for example, it
has been customary to use two different solvents, a first solvent
in which the epoxy resin, the graft polymer, and the addition
polymer are all soluble, and a second solvent that can dissolve the
addition polymer product and that can solvate the addition polymer
side chains of the graft polymer. The solvents remain with the
resinous reaction product after it is dispersed by the addition of
water and a fugitive base, and more may be added to adjust
application characteristics. A typical ratio of total organic
solvent to total film-forming resinous solids (OS/S) is about 0.9,
in a formulated, sprayable, sanitary coating composition.
Consequently, when an applied coating is cured, which is usually
accomplished by heating, the solvent is driven off and ordinarily
escapes into the atmosphere. With the present concern over the
release of organic solvent materials into to atmosphere, it is
highly desirable that coating compositions be prepared in such
manner as to reduce the amount of organic solvent liquid present to
the smallest feasible amount.
In the fifth patent application referred to above, Ser. No. 29,106,
filed Apr. 11, 1979, coating compositions and processes for making
them were disclosed that advanced the art by providing compositions
having the functional characteristics adverted to in connection
with the inventions described above in the other co-pending
applications, but containing a greater proportion of addition
polymer, thereby permitting economies, and also containing a
smaller proportion of volatile organic solvent, thereby
facilitating compliance with environmental protection laws.
Improved water-reducible coating compositions are made in
accordance with this application by polymerizing in situ, in an
aqueous dispersion of a resinous reaction product produced in
accordance with a process of one of the earlier-filed patent
applications described above, a limited quantity of addition
polymerizable monomer containing ethylenic (vinyl) unsaturation,
such as styrene. The result is to reduce substantially the
percentage of the final composition solids represented by the
initial epoxy resin, and to increase substantially the percentage
of the final composition solids formed from ordinarily much less
expensive addition polymerizable monomer. The resulting increase in
solids and decrease in the proportion of solvent are important
advantages. Moreover, the proportion of solvent may be further
reduced by the addition of water during or after the in situ
addition polymerization reaction. A typical OS/S ratio would be
about 0.7, for a fully formulated sprayable sanitary coating
composition.
The addition to the dispersed, graft polymer-containing resinous
reaction product, of vinyl polymers formed by the in situ
polymerization reaction, offers a still further advantage, namely,
an improved set of physical and chemical characteristics for
certain applications, important among which is improved resistance
to weathering.
BRIEF SUMMARY OF THE INVENTION
In its broadest aspects, this invention provides new and improved
polymeric products and processes for making them, and new and
improved coating compositions and processes for making them,
especially water-reducible coating compositions that are
characterized by desirable application and functional properties,
very low solvent release to the atmosphere, and economical
formulation.
A first preferred mode of the process of the invention involves
these steps:
1. Forming a fluent blend of an aromatic epoxy resin with an
extender polymer in an organic solvent, preferably substantially
free from particulate matter. The extender polymer may be a (Type
A, saturated) material such as:
a. polystyrene;
b. low molecular weight polyethylene;
c. a styrene-acrylate copolymer;
d. an ethylene-vinyl acetate copolymer;
e. a hydroxyl-terminated polyester or polyurethane;
f. styrene-acrylonitrile copolymers;
g. almost any hydrocarbon resin;
h. a second epoxy resin, selected for its properties, cost, or the
like, or
i. a mixture of one or more of these.
2. Advancing the epoxy resin with a diphenol or other
polyfunctional extender, generally at a temperature in the range
from 130.degree. C. to 250.degree. C. The extent of the advance is
controlled so that the mix remains tractable. When a polyglycidyl
ether of bisphenol A is advanced by reaction with bisphenol, a
temperature of about 180.degree. C. is a useful reaction
temperature. However, when a hydroxyl-terminated polyester is
employed as all or a substantial proportion of the extender, then a
higher temperature, about 220.degree. C., is used. The advancement
in any case is arrested at a desired stage, by cooling, reacting
some or all of the epoxy groups, or the like.
3. Adding ethylenically unsaturated monomer together with at least
3% by weight of the monomer of benzoyl peroxide, or equivalent
peroxide-type initiator, and raising the temperature as needed to
activate the initiator. In a preferred embodiment, the monomer
contains enough of an acrylic acid to contribute at least 5% by
weight of carboxyl (COOH) groups to the total solids present. There
must be enough ionizability, through acid or base functionality,
that the material can be established as a dispersion in a basic
aqueous vehicle.
4. Adding water and an ionizing agent, to disperse all of the
polymer solids in the aqueous vehicle
5. Performing a vinyl polymerization in situ, preferably with
styrene or with styrene and an acrylic acid. Sufficient
ionizability must still be present to permit dispersion
formation.
This process produces a dispersion that may be further diluted with
water. It may also be formulated with pigments, a cross-linking
agent, and the like, for application as a decorative and protective
coating.
Steps 1 and 2 above prepare a grafting base, by blending a
1,2-epoxy resin having an epoxy equivalent weight (EEW) of at least
180-200, and preferably 500 or more, with a second, extender
polymer, mixing the resin and the polymer with an organic solvent
to form a fluent blend, and then advancing the epoxy resin in the
presence of the extender polymer. The epoxy resin is advanced by
reacting it with a polyfunctional compound that adds to the epoxy
resin at its epoxide groups, to advance the resin to a higher
molecular weight. The polyfunctional compound is preferably either
a polyhydroxy compound or a polycarboxylic acid.
The grafting base may be one prepared in the manner described in
the preceding paragraph, or it may be one prepared by blending
together in a solvent an epoxy resin of suitable epoxy equivalent
weight, preferably above 500, and more preferably not substantially
below 2,000, and the extender polymer.
In a second preferred mode of the process of the invention, the
extender polymer employed contains ethylenic unsaturation (Type B,
unsaturated). It therefore offers convenient points of attachment
for the later-added monomer, so that side chains may develop at
each ethylenically unsaturated site. Looked at another way, it
could be said that copolymerization occurs. Suitable such extender
polymers include polybutadiene, unsaturated polyesters, unsaturated
alkyds, polyisoprene, butadiene-styrene polymers, and acrylated
resins that are ethylenically unsaturated. Except for the selection
of the extender polymer, the steps are essentially the same as
stated above. However, the chemical structures in the resulting
grafting base are more complicated and diverse.
Both the epoxy resin and the extender polymer components of the
grafting base should provide aliphatic backbone carbon atoms having
one or two hydrogens bonded thereto in the ungrafted state, at
which grafting can occur in the third, grafting step. Also, the
extender polymer should be selected to be a film-former that
remains in the film after baking at a temperature of at least
375.degree. F. (190.degree. C.). Preferably it is soluble in the
solvent used. Generally, it is inert to the epoxy resin and to the
advancing agent but it may simply be relatively inactive as to the
epoxy resin and substantially less reactive to the advancing agent
than the epoxy resin at the temperature used for advancement, which
generally is in the range from about 120.degree. C. to about
200.degree. C.
The second step of advancing the epoxy resin includes the step of
arresting the advancement. This may be either an active step,
involving cooling, for example, or a passive step, i.e., complete
consumption of the reactants, or a combination of both.
The third step involves polymerizing ethylenically unsaturated
monomer in the presence of the grafting base, and in the presence
of an initiator. When the extender polymer is a Type A, saturated
polymer, this step is carried out in the presence of at least 3%
and preferably more than 4% by weight, based on the monomer weight,
of benzoyl peroxide (BPO) or other suitable peroxide-type initiator
that has the ability simultaneously to initiate (1), addition
polymerization of the monomer through its ethylenic unsaturation,
and (2), graft polymerization of addition polymer to aliphatic
backbone carbon atoms of the epoxy resin and of the extender
polymer. Suitable initiators must be capable of initiating addition
polymerization through ethylenic unsaturation. When extender
polymer is saturated, the initiator also must have the ability to
abstract hydrogen from a backbone carbon, to permit
carbon-to-carbon grafting to occur.
When the extender polymer is Type B, unsaturated, the same
considerations apply, subject to the proviso that less than 3% of
the initiator may be needed since the reaction involves the
unsaturated extender polymer as well as the epoxy resin.
Consequently, the amount of initiator may be substantially as low
as would suffice for initiating the addition polymerization and
abstracting hydrogen and causing grafting in that manner. However,
the use of a peroxide-type, hydrogen abstracting initiator, in an
amount of at least 3% BPO or equivalent, is preferred; it is
believed that this preferred mode induces grafting on both the
epoxy resin and the extender polymer, whether the extender polymer
is saturated or unsaturated.
The products of the process described in the preceding paragraph
(the third step), like the grafting base, are novel and are useful
in and of themselves. For example, the grafting base and these
resinous reaction products can be formulated into useful
solvent-based coating compositions for either air drying or
baking.
Provided that the third step product contains a sufficient number
of ionizable sites so that it is emulsifiable, as is preferred, it
can be dispersed, as in the fourth step, in an aqueous vehicle
containing an ionizing agent to make a water-reducible,
dispersion-type coating composition. Such an aqueous dispersion is
also a useful vehicle in which vinyl monomer can be polymerized in
situ, as in the fifth step, to increase the solids content of the
dispersion, and at the same time to decrease the relative
proportion of organic solvent. The end product of this fifth
process step is a water-reducible aqueous dispersion that is
suitable for a variety of coating applications. In preferred
embodiments, such compositions are sprayable and are useful for
lining beverage cans.
A third preferred embodiment of the invention involves a variation
in the order of the steps, as follows:
1. Advancing the epoxy resin (if necessary).
2. Addition polymerizing-grafting (as in Step 3 above).
3. Dispersing in an aqueous vehicle (as in Step 4 above).
4. Adding to the dispersion an extender resin.
5. Performing a vinyl polymerization in situ.
This variation embodiment of the invention is less preferred. If
the extender polymer is saturated, there is less opportunity for
grafting to occur, although some grafting seemingly does occur in
the fifth, final step. If the extender polymer is unsaturated, then
grafting will occur. This third process mode can of course be
combined with each of the two process modes already described,
which also can be combined with each other. As described in greater
detail hereafter this variant process embodiment also produces
water-reducible products that can be formulated into valuable
coating compositions.
DETAILED DESCRIPTION OF THE PRIOR INVENTIONS; PROCESS AND
PRODUCT
The prior inventions are most easily understood from a description
of one specific preferred embodiment.
When making a sanitary coating composition in accordance with one
preferred embodiment of one of the earlier patent applications
described above, for example, Ser. No. 788,611, 70 to 80 parts by
weight of an aromatic 1,2-epoxy resin are placed in a reaction
vessel with a small amount of a solvent, such as, for example,
2-butoxy-ethanol-1. The epoxy resin may be purchased and used as
is, in which case an initial epoxy equivalent weight (EEW) of about
4,000 is preferred, or alternatively, a low EEW resin may be
reacted further with bisphenol A to produce an epoxy resin having
the desired EEW of about 4,000.
A mixture of monomers containing ethylenic unsaturation is then
prepared. In one preferred embodiment, this mixture is formed from
about 65 weight percent methacrylic acid, 34 weight percent
styrene, and 1 weight percent ethyl acrylate. Benzoyl peroxide
(BPO) is incorporated in the mixture in an amount equivalent to
about 6.7% of the monomer mixture by weight. This mixture is then
added to the reaction vessel containing the epoxy resin over a
period of time, at a temperature in the range from 110.degree. C.
to about 130.degree. C., preferably about 115.degree. C. to
120.degree. C., and more preferably about 118.degree. C., to permit
the reaction to go forward. Sufficient butanol and
2-butoxy-ethanol-1 are added to facilitate agitation.
It is very difficult to make an accurate analysis of the reaction
product that is obtained. However, current indications are that on
a dry solids basis, the reaction product contains three different
components, as follows:
1. about 38% of unreacted epoxy resin;
2. about 7% by weight of ungrafted addition polymerized monomer,
and
3. about 55% of a graft polymer, in which 65% of the original
addition polymerizable monomer has polymerized and grafted to about
53% of the original epoxy resin.
All of these values are approximations due to limitations in
analytical techniques.
Studies on this reaction and the product produced indicate that
grafting takes place at aliphatic backbone carbons of the epoxy
resin that have either one or two hydrogens bonded thereto in the
ungrafted state. Pictorially, bonding takes place at one of the
carbons indicated by the arrows below: ##STR1## The graft polymer
product consists of an epoxy resin molecule, of about 8,000
molecular weight, grafted with, on the basis of statistically
averaged information, about two short chains of addition copolymer
per molecule of epoxy resin, the molecular weight of each chain
being about 1,500, so that the molecular weight of the graft
polymer itself is about 11,000. This structure is one that can be
represented generally as follows: ##STR2##
Gel permeation chromotography indicates that the molecular weight
of the unreacted epoxy resin in the final product is somewhat lower
than that of the initial epoxy resin, indicating that higher
molecular weight epoxy resin tends to be grafted preferentially.
This probably occurs because there are more grafting sites per
molecule in the higher molecular weight epoxy resin molecules. The
available analytical data also indicates that during the
polymerization of the mixture of addition polymerizable (vinyl)
monomers, very little homopolymer is formed, and that the ungrafted
acrylic copolymer has a longer chain length (higher molecular
weight) than the grafted acrylic copolymer.
The resinous reaction product, which is a mixture of the three
components described above, has an Acid Number of about 85, and a
percent oxirane oxygen content, as determined by the analytical
method described in the patent applications described above, of
about 0.35, or less.
During the manufacturing process, the solvent content of the
product is adjusted periodically so that in this preferred
embodiment, the final product is about 58%-60% by weight solids,
the balance being a solvent system consisting of a mixture of
n-butanol and 2-butoxy-ethanol-1.
To prepare a coating composition useful for spray application to
cans for beverages, the resinous reaction product is mixed with
deionized water and a fugitive base, which in the preferred
embodiment is dimethyl ethanolamine. Sufficient water is employed
so that the non-volatiles content of the composition is about 21%
to 24%, with a pH of about 7.8. About 10% to 11% by weight of the
initial epoxy resin of a suitable crosslinking aminoplast resin,
such as, for example, Cymel 370, a product of American Cyanamid
Company, is then added. After thorough mixing, the resulting
dispersion remains stable on storage indefinitely. It sprays
readily with particularly good application properties. It cures
rapidly on baking. The coatings produced are bland, and do not
impart any undesirable organoleptic property or haze to a canned
beverage or other food product.
The difficulty in analyzing the resinous reaction product obtained
from the graft polymerization step cannot be overemphasized.
Moreover, the composition of the product obtained depends upon the
initial molecular weight of the epoxy resin, the proportions of the
reactants, and the amount of BPO or equivalent initiator employed,
among other factors. Consequently, for the preferred embodiment
described above, the analytical data reported should be understood
to be approximate. The proportion of the molecular weight of the
graft polymer that is contributed by the addition polymer side
chains is particularly difficult to determine, but probably is in
the range from about 16% to about 20%, for this particular,
preferred embodiment.
One of the interesting properties observed, as to the resinous
reaction product, is that its Tg is about 30.degree. C.-65.degree.
C. This compares with much higher Tg values for the initial epoxy
resin component; for a copolymer that is prepared by the addition
polymerization of a monomer mixture such as was used; and for a
mixture of the initial epoxy resin with such a copolymer; the Tg
values for these being, respectively, generally in the range from
about 80.degree. C. to 85.degree. C.; about 110.degree. C.; and
about 75.degree. C. to 80.degree. C.
For other embodiments of the invention than the can coating
embodiment just described, the particular components employed, and
their proportions, for making the resinous reaction product
containing the graft polymer, are subject to a broad discretion,
depending upon the intended application. The epoxy resin may have a
molecular weight in the range from about 350 to about 40,000 or
higher, the limiting factor being the ability to handle the epoxy
resin on a practical basis. The amount of epoxy resin may be in the
range from about 5% by weight to about 95% by weight of the initial
reaction mixture, dry solids basis.
To make a preferred sprayable sanitary coating composition, the
molecular weight of the epoxy resin, preferably a diglycidyl ether
of bisphenol A, generally is in the range from 4,000 to 20,000, or
higher, or more preferably for practical manufacturing processing,
in the range from about 8,000 to 12,000 or so. The proportion of
epoxy resin in the initial reaction mixture preferably is from
about 60% to about 90% by weight, and more preferably, 70% to 80%.
Sufficient methacrylic acid or the equivalent should be employed in
the monomer component so that the Acid Number of the resinous
reaction product, based on solids, is in the range from 80 to 90.
For use it is dispersed in water with an amine ionizing agent, and
preferably a cross-linker is added. The coating is baked to cure
it, and to drive off fugitive ionizing agent.
For all of these and other coating applications, the amount of
benzoyl peroxide or other equivalent initiator employed in the
grafting-addition polymerization reaction should be above 3% by
weight based on the monomer, preferably more than 4% and most
preferably in the range from about 6% to 7%. This permits the use
of reaction temperatures in the range from about 110.degree. C. to
about 130.degree. C., preferably about 115.degree.-120.degree. C.,
for efficient operation. If the epoxy resin is terminated, however,
higher reaction temperatures and other peroxide-type initiators can
be employed. If active epoxy groups are present, temperatures above
about 130.degree. C. tend to favor ester formation, rather than
carbon-to-carbon grafting.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
The following description, until indicated otherwise, refers to the
first, preferred embodiment of the process of this invention.
FIRST PREFERRED EMBODIMENT
Steps 1 and 2
The Grafting Base
To make the novel grafting base, an aromatic or aliphatic epoxy
resin, preferably an aromatic 1,2-epoxy diepoxide resin is blended
with the extender polymer and organic solvent. The term "epoxy
resin" as used herein is intended to encompass those aliphatic
and/or aromatic resins which may be defined as polyethers
containing terminal oxirane groups. In the usual and preferred
case, the epoxy resin will be a diglycidyl polyether of bisphenol A
or a similar diphenol, in which the terminal oxirane groups are
separated by alternating aromatic and aliphatic units.
The two polymeric materials, either before or after being blended
together, are generally mixed with an organic solvent which
facilitates handling of the blend, and preferably in which the
blend is soluble. This mixture should be fluent, i.e., easily
stirred, and while it may be a slurry, it preferably forms a clear
solution free from particulate resinous material. The terms
"fluent" and "tractable" refer to the ability to mix on a practical
basis with conventional mixing equipment such as a turbine or
propellor mixer. At 180.degree. C., this means that the viscosity
would be about 200,000 cps. maximum.
The epoxy resin is then advanced by reaction with a polyfunctional
compound that adds to the epoxy resin at its epoxide groups, to
increase its epoxide equivalent weight (EEW). This polyfunctional
advancing agent generally will either not react with the extender
polymer, or will react preferentially with the epoxy resin.
The extender polymer often is a saturated hydrocarbon polymer, such
as a low molecular weight polyethylene, i.e., a polyethylene oil,
grease, or wax, or polystyrene, polyisobutylene, or the like. This
polymer, like the epoxy resin, preferably is one that has aliphatic
backbone carbons that have either one or two hydrogens bonded
thereto in the ungrafted state. Thus, low molecular weight
hydrocarbon polymers such as those mentioned above, and in
addition, other low molecular weight polymers such as
polypropylene, copolymers of polyethylene, copolymers of
polypropylene, poly(4-methylpentene-1), poly-alpha-methylstyrene,
and other such hydrocarbon polymers are suitable for use.
Also suitable are acrylate polymers and copolymers such as
styrene-acrylate copolymers, styrene-allyl alcohol copolymers,
hydroxy-terminated polyurethane resins, and ethylene-vinyl acetate
copolymers. Hydrocarbon resins such as polyindene, naphthalene
polymers, and the like, are also useful. Polycoumarone and
coumarone-indene resins may also be used.
The extender polymer may also be an epoxy resin, selected for
example for special properties or for low cost. Thus epoxidized
polybutadiene may be used. If desired, when an epoxy resin is used
as the extender, some or all of the epoxy groups may be removed by
chemical modification.
If the extender resin is one that is reactable with epoxy groups at
temperatures on the order of those used in the advancement
reaction, as would be the case with an acid-containing polyester,
then a lower advancement temperature might be required. The
modification of epoxy groups with benzoic acid or the like, in the
presence of an extender resin such as a polyester, might lead to
cross-linking to the epoxy group sites.
The polyfunctional compound that is employed to advance the epoxy
resin may be an aromatic polyhydric alcohol, preferably a
polynuclear polyhydroxy phenol; an aliphatic polyhydric alcohol; or
a polycarboxylic acid, either of the saturated aliphatic kind or
the cyclic unsaturated or aromatic kind. Particularly suitable
aromatic polyhydric alcohols include bisphenol A, bisphenol F,
novolac resins, and materials such as polyhydroxy diphenyl sulfone.
Suitable aliphatic polyhydric alcohols include ethylene glycol,
glycerol, butanediol, erythritol, polyethylene glycol,
polypropylene glycol, including specifically such glycols as
triethylene glycol, and the like. Suitable polycarboxylic acids and
acid anhydrides are those of adipic, azelaic, sebacic, and succinic
acids. Suitable cyclic acids include tetrahydrophthalic acid,
hexahydrophthalic acid, and phthalic acid.
The organic solvent that is employed may be added, or, if the epoxy
resin and the hydrocarbon polymer happen to be available in
solution form on a commercial basis, it may be that the solvent
already present will suffice. The epoxy resins are often available
in liquid form at low molecular weights, or in solution form, at
either low or moderately high molecular weights. Otherwise, a wide
variety of solvents can be employed to dissolve or slurry the
resins. A particularly preferred solvent is 2-butoxy-ethanol-1.
This material is also a good solvent for many of the hydrocarbon
extender polymers (both saturated and unsaturated) that are
suitable for use in the present invention.
The extender polymer selected must be capable of dissolution in a
solvent. This places an inherent limitation on the molecular weight
of many of the extender polymer materials, such as, for example,
polyethylene and polypropylene.
While the epoxy resin may have an EEW as low as about 180 to 200,
such a resin does not have many aliphatic backbone carbon atoms
suitable for grafting. Accordingly, it is preferred that the epoxy
resin be a polyglycidyl ether of a bisphenol, preferably a
diglycidyl ether of bisphenol A, and have an EEW of at least 500,
and more preferably, not substantially below 2,000. Such preferred
epoxy resins provide a number of available grafting sites.
The epoxy resin may contribute from 10% to about 90% or more by
weight of the solids initially present in the mixture for making
the grafting base. The balance of the solids for the grafting base
is contributed by the extender polymer or by a mixture of suitable
such polymers.
As a practical matter, at present water-reducible coating
compositions from the fifth step would be designed for use for
coating metal surfaces, because of the good wetting, adhesion, and
barrier characteristics imparted by the epoxy resin. Consequently,
in order that the characteristics of the epoxy resin may be
apparent in the final coating composition products, the epoxy resin
employed generally should contribute at least 5% and preferably at
least 20% by weight of the total solids in the final product.
Generally, the final product (from step 5) may contain as little as
5% by weight of solids derived from the initial epoxy resin for
such applications as a wood paint. For metal protective and
decorative coatings, the epoxy resin should contribute at least 20%
and preferably about 25%, and more preferably a minimum of 30% to
40% of final product (from step 5) solids, depending on the
properties desired and those contributed by the extender polymers,
with an upper limit of about 60% representing all that is required
for the attainment of most desirable functional properties. Greater
amounts of epoxy resin may be present, of course.
The desirable functional properties imparted by the epoxy resin
include not only wetting and adhesion properties, but also the
ability to form good barrier films, as between a can and its
contents. Moreover, if the adhesion to the substrate is strong
enough, the coating will act as though it were flexible (even
though in fact it may not be). This is important in some types of
fabrication where the substrate is coated first, then shaped
mechanically while coated. Obviously the demands on coatings in
such applications are severe. For sprayable sanitary coating
composition materials (from step 5), an epoxy resin contribution to
total solids of from 30% and preferably 40% to 60% is feasible, and
with careful formulation and for good economy, from 45% to 50% is
preferred at present, and represents an important formulating
accomplishment of the present invention.
These final product figures are important with respect to the
initial proportion of epoxy resin that must be present in the
grafting base.
The proportion of total solids present to organic solvent in the
initial mixture of epoxy resin and extender polymer, from which the
grafting base is made, may be as little as is required to permit
suitable handling for practical manufacturing operations. However,
while the grafting base must be fluent or tractable to permit it to
be worked in practical manufacturing operations, this
characteristic can be derived from the use of an elevated
temperature and not just from the use of solvent alone. The
proportion of solvent used will depend upon the characteristics of
the epoxy resin and of the extender polymer employed. Generally the
practical limit is about a 60% concentration of solids in the
solvent. While lower solids concentrations are usable, one of the
objectives of the invention is to reduce the organic solvent
content of the final product, and accordingly, a preferred
operating range for solvent concentration in the grafting base is
from about 40% solvent to about 60% solvent.
The third step of the process of the present invention, described
below, is a grafting reaction. One feature of this reaction is the
use of an unusually high proportion of free radical initiator
relative to addition polymerizable monomer that is used in the
reaction. The free radical initiator must be one that has hydrogen
abstraction capability, to induce the formation of carbon-to-carbon
bonding at aliphatic backbone carbons of the advanced epoxy resin
and of the extender polymer, in the grafting base. The preferred
free radical initiator for this purpose is benzoyl peroxide.
The benzoyl peroxide is employed at an elevated temperature in
order to activate it. A temperature of 110.degree. C. to
130.degree. C. is preferred, and a more preferred operating
temperature is one in the range from about 115.degree. C. to about
120.degree. C. In this operating temperature range, the benzoyl
peroxide decomposes, forming, as one by-product, benzoic acid.
There is a tendency for the benzoic acid to react with the epoxy
groups of the epoxy resin, to form epoxy esters, and if the monomer
used includes a carboxylic acid, it also may form esters.
To avoid or reduce ester formation and particularly, ester
grafting, the epoxy resin may be reacted, when preparing the
grafting base, with enough chemical terminating agent to eliminate
the epoxy groups in part or substantially completely. Materials
that are generally useful as terminating agents for the epoxy
groups include the phenols, many of the carboxylic acids, primary
and secondary amines, mercaptans, alcohols, and water.
Ethylenically unsaturated terminating agents can be used, and will
lead to addition polymerization reactions during the subsequent
grafting step.
Bisphenol A is a preferred terminating agent for advancing the
epoxy resin. For example, slightly less than 64 weight parts of Dow
DER 333 liquid epoxy resin per 36 weight parts of bisphenol A, to
about 60 parts of the DER 333 liquid epoxy resin per 40 weight
parts of bisphenol A, represents a useful range for these
particular reactants. One preferred terminated epoxy resin is a
diglycidyl ether of a bisphenol, wherein the molar ratio of the
diglycidyl ether to the bisphenol is from about 1.7 to about
1.5.
Other hydroxy materials that are useful as terminating agents
include the cresols and the xylenols. Saturated fatty acids and
aromatic monocarboxylic acids, such as benzoic acid, are
particularly useful terminating agents, but like the monohydroxy
compounds, they terminate without advancing the resin. They are
thus useful in the present invention for terminating an epoxy resin
that is at a desired molecular weight, and if used, preferably are
used prior to the grafting reaction. Ordinarily the fatty acids can
be used in a variety of commercial forms and need not be highly
purified. However, acids such a palmitic, lauric, myristic, and
stearic are very useful, in either refined form or as highly
purified acids.
The primary and secondary amines are also useful terminating
agents, and particularly, hydroxyl amines such as, for example,
ethanolamine and diethanolamine. Tertiary amines are generally not
suitable terminating agents, since they lack the presence of a
labile hydrogen atom reactable with the epoxy group.
Some representative grafting base compositions, in terms of the
solids present, are described in Tables 1A and 1B below. Each of
the grafting bases described in these tables can be used in the
practice of the invention. If at least about 40% by weight of the
solids present in the final product are to have been contributed by
the initial epoxy resin, then in practice careful control must be
exercised in the grafting (third) step and in the in situ
polymerization (fifth) step as to the amount of contributed to
total solids by each of these steps.
TABLE 1A ______________________________________ Representative
Grafting Base Solids Compositions Extender Epoxy Resin Component
Polymer Component Grafting % by Weight % by Weight Base Based on
Based on No. Solids Identity* Solids Identity*
______________________________________ 1-1 95 A 5 K 1-2 95 A 5 L
1-3 95 A 5 N 1-4 94.4 B 5.6 O 1-5 85 B 15 N 2-1 80 A 20 K 2-2 80 A
20 L 3-1 70 A 30 L 3-2 70 A 30 N 4 50 A 50 K 5-1 40 A 60 K 5-2 40 A
60 L ______________________________________ *See Table 1B for the
identities.
TABLE 1B ______________________________________ Identities of Table
1A Solids Materials ______________________________________ Epoxy
Resin Code for Epoxy Resin Estimated Approx. Component Composition
Mol. Wt. ______________________________________ A Dow DER-333 9,000
epoxy resin advanced with bisphenol A (manufacturer's (65/35)
figure) B liquid epoxy 5,000 (approx.) resin advanced with (oxirane
bisphenol A termination) ______________________________________
Extender Polymer Code for Extender Polymer Component Composition
Approx. Mol. Wt. ______________________________________ K
polystyrene 15,000 (approx.) L polybutene 24 950 (Chevron Chemical
Co.) N Cumar-R-1 730 (Coumarone-indene polymer from Neville
Chemical Co.) O epoxidized polybutadiene 700-800
______________________________________
STEP THREE
THE GRAFTING REACTION: A, GENERAL
Enough solvent is employed to facilitate handling. The amount and
kind of monomer to be employed will depend upon several factors.
These include the proportions and identities of the epoxy resin and
of the extender polymer in the grafting base, and the proportion
and ionizability of the monomer to be added by the subsequent in
situ vinyl polymerization step. Typical amounts of monomer to be
added in this grafting step would be in the range from 5% to 50% by
weight of the grafting base.
Any free radical source capable of hydrogen abstraction may be used
as a catalyst (initiator). The preferred initiator is benzoyl
peroxide. It is effective when used a concentration of at least 3%
by weight of the monomer and at a temperature of about 100.degree.
C. to generally not above 130.degree. C. Preferably the
concentration is above about 4% based on monomer, and the
temperature is in the range from 110.degree. C. to 120.degree. C.
Most preferably, the concentration of benzoyl peroxide is from 6%
to 7% based on monomer. Mixtures of peroxide-type initiators may
also be used.
When the epoxy resin has been terminated, with the elimination of
substantially all of the epoxy groups, there is no danger of an
esterification reaction occurring between the epoxy resin and any
ethylenically unsaturated carboxylic acid in the monomer component,
or any acid decomposition product from the initiator. Accordingly,
higher reaction temperatures may be employed for the
grafting-addition polymerization reaction, and a wider variety of
initiators may be employed, requiring or permitting the use of a
much broader range of reaction temperatures. For example, dicumyl
peroxide can be used at reaction temperatures of about 140.degree.
C. to 160.degree. C., or even higher.
Examples of other initiators are alkyl peroxy esters, alkyl
peroxides, alkyl hydroperoxides, diacyl peroxides, t-butyl
perbenzoate, lauroyl peroxide, dicumyl peroxide, decanoyl peroxide,
and caproyl peroxide.
The term "graft polymer resinous reaction product" and the briefer
"resinous reaction product" are used to refer to the reaction
mixture that is produced by this step. The epoxy resin and extender
polymer preferably each have aliphatic backbone carbons having one
or two hydrogens bonded thereto in the ungrafted state. In the
presence of at least 3% benzoyl peroxide (BPO) or equivalent
hydrogen-extracting initiator, based on monomer, the monomer is
polymerized and simultaneously grafted at one or more of these
backbone carbons, on the epoxy resin and, it is believed, on the
extender polymer as well.
The resinous reaction product is believed to be properly
characterized as a mixture of unreacted epoxy resin, unreacted
extender polymer, and three other associatively-formed polymers.
One of these associatively-formed polymers is the epoxy-based graft
polymer. A second, Graft polymer is believed to be formed on the
extender polymer. The third associatively-formed polymer is
ungrafted addition copolymer.
The grafting reaction has several important results: an increase in
the solids content of the mixture, with a relatively low cost
material; a modification of the characteristics of the components
of the grafting base, by the introduction of a different component
that influences product characteristics in a desirable way,
particularly with respect to hydrolytic stability, and weathering
and mechanical properties; an increase in the compatibility of
those residual reactants present that are not grafted and that are
otherwise mutually incompatible, in the solid state. This last
point is particularly important with respect to unpigmented films
formed from the products of this step, where clarity and
transparency are important and where the presence of incompatible
phases would lead to haziness or worse.
Another important result of the grafting reaction is the
introduction of sites that are ionizable. The ionizable sites may
be either anionic or cationic, depending upon the nature of the
monomer component. For sanitary coating applications, they are
anionic.
A concomitant result is that those sites along the backbones in the
grafting base, that are most susceptible to attack, are preempted
and occupied thus improving the resistance of the product to
chemical attack.
Since the grafting reaction is effected by carbon-to-carbon
bonding, the graft polymers produced are not susceptible to
hydrolysis.
THE GRAFTING REACTION: B, ACID-FUNCTIONAL RESINOUS REACTION
PRODUCTS
The vinyl monomer may be a single monomer but preferably is a
monomer mixture. To make an acid-functional product, ethylenically
unsaturated acids, particularly acrylic acid and methacrylic acid,
are preferred components. Styrene is a valuable monomer for use
because it is economical and has other desirable properties.
Ethylenically unsaturated acid esters are also useful, such as, for
example, ethyl acrylate, butyl acrylate, the corresponding esters
of methacrylic acid, and the like.
The ethylenically unsaturated acids include true acrylic acid and
lower alkyl substituted acrylic acids, that is, those acids having
ethylenic unsaturation in a position that is alpha, beta, to a
single carboxylic acid group. The preferred acrylic acid is
methacrylic acid.
The monomer component will preferably contain a major proportion of
an acrylic acid, preferably methacrylic acid. When a styrenic
monomer such as styrene is employed, it constitutes, ordinarily, a
minor portion of the monomer component. For those coating
compositions that may come in contact with food, and for the
preparation of beverage can coating compositions in particular, one
preferred addition polymerizable monomer mixture is made from 70
parts by weight of methacrylic acid to 30 parts by weight of
styrene to 1 part by weight of ethyl acrylate. Another preferred
monomer mixture includes methacrylic acid, styrene, and ethyl
acrylate, in the approximate weight ratio of 65:34:1
respectively.
THE GRAFTING REACTION: C, BASE-FUNCTIONAL PRODUCTS
Base-functional resinous reaction products may be made by
incorporating an amine in the graft polymer molecule. There are two
preferred ways to do this.
First, an unsaturated amine, such as dimethylaminoethyl
methacrylate or t-butyl amino ethyl methacrylate, is employed in
the monomer mixture that is used to form the graft polymer resinous
reaction product. In this case, the balance of the monomer mixture
comprises monomer materials such as styrene, lower alkyl acrylates,
hydroxyethyl acrylate, and the like.
Second, a material such as glycidyl methacrylate is included in a
monomer mixture that does not include other functional monomers.
This introduces epoxy groups into the side chains of the graft
polymer product, and these can be reacted with primary or secondary
amines, to make the graft polymer (and ungrafted addition
copolymer) base functional.
In addition, if the ungrafted epoxy resin and the epoxy resin
component of the graft polymer have terminal epoxy groups available
for reaction, they may be reacted with primary or secondary amines,
to impart some base functionality.
THE GRAFTING REACTION: D, THE RESINOUS REACTION PRODUCT
The solids produced by the grafting reaction should contain a
sufficient number of ionizable sites so that when added to an
aqueous medium containing an ionizing agent, the solids become
established as a dispersion in the aqueous medium. The
dispersibility or solubility of the product depends upon the
strength and degree of ionization. The dispersibility should be at
least sufficient that the entire resinous reaction product is
readily dispersed in the aqueous vehicle in which ionization
occurs.
Generally, where carboxylic acid monomer units are responsible for
acid functionality, these units should constitute at least 5% by
weight of the resinous reaction product of the grafting reaction,
and preferably, at least about 10% or so. It is best to combine the
weight percent of carboxylic acid units with a measurement of the
Acid Number value for the resinous reaction product, based on
non-volatiles (N.V.). Also, since some carboxylic acid units may be
consumed during a grafting reaction, as by ester formation with
epoxide groups, a second measure of acid functionality, such as
Acid Number (N.V.), provides a better indication of ionizing
potential. Generally, the Acid Number of the resinous reaction
product of the grafting reaction should be in the range from 30 to
220, and preferably from 45 to 150.
In the case where the resinous reaction product of the grafting
reaction is base-functional, a convenient indicator of ionizable
potential is the tertiary amine nitrogen content, or the equivalent
and the useful range is from about 0.1% tertiary amino nitrogen to
about 5% tertiary amino nitrogen. A secondary amine nitrogen can be
ionized, but has less effect. A tertiary amino nitrogen can be
ionized by an acid, such as hydrochloric, lactic, or acetic acid,
or by a quaternizing agent such as dimethyl sulfate. When the
ionization is derived from quaternary nitrogen, a lower nitrogen
content is needed for the same result than is the case where the
ionization is derived from tertiary amine nitrogen.
SECOND PREFERRED EMBODIMENT
Steps 1, 2, and 3
The Grafting Base, and the Grafting Reaction
In the second preferred process for preparing a grafting base, the
extender polymer contains ethylenic unsaturation. Polybutadiene is
the preferred material in this category.
The ethylenic unsaturation offers a site at which side chains can
attach during the addition polymerization-grafting step, in place
of or in addition to grafting to the epoxy resin backbone.
Similarly, further homopolymerization, or copolymerization with the
addition polymerizable monomer, may occur. Also, all of these may
occur at the same time. In fact, all of these possible addition
polymerization reactions appear to occur, simultaneously with
grafting to the epoxy resin. The limited evidence that is available
indicates that all of these reactions do occur at once, especially
where relatively high (25%) amounts of the extender polymer are
present, and that simultaneously, grafting takes place by the
attachment of side chains on the epoxy resin backbone, just as
though the extender polymer were not present. That such grafting
does occur is demonstrated by the stability of the aqueous
dispersions that are obtained in the next step, and by the fact
that films cast from either solutions or dispersions of the
resinous reaction products are clear and free from haze.
Except for the composition of the grafting base, and subject to the
above, the grafting reaction and the dispersion and in situ vinyl
polymerization steps (Steps 4 and 5) are substantially the
same.
Some representative grafting base compositions are described in
Table 2 below.
TABLE 2 ______________________________________ Representative
Grafting Base Solids Compositions Second Preferred Embodiment Epoxy
Resin Component Extender Grafting Polymer Component Base % by
Weight % by Weight Nos. Based on Solids Identity Based on Solids
Identity ______________________________________ 6-1 85 B* 15 M**
6-2 70 A* 30 M ______________________________________ *See Table 1
B above **M is polybutadiene (Lithene P.sub.1, Rivertex Corp.) with
an approximat molecular weight of 900.
STEP FOUR
Dispersion in an Aqueous Medium
The term "aqueous dispersion" as used herein is intended to
encompass both solutions and dispersions. Solutions generally
require a higher degree of ionization than is practical or needed.
This invention is primarily concerned with true dispersions, which
may be defined as suspensions of colloidal or larger particles in
an aqueous medium.
To form the resinous reaction product of the grafting reaction into
an aqueous dispersion, it is mixed with water containing an
ionizing agent. For this reason, the solvents used should be
water-miscible.
For an acid-functional product, a fugitive base is used as the
ionizing agent. For a base-functional product, the ionizing agent
may be a fugitive acid, such as acetic acid. A fugitive ionizing
agent is one that volatilizes at the curing temperature for the
product, leaving no appreciable residue.
To convert a reaction mixture to an aqueous suspensions, the
techniques employed are essentially conventional. An acid
functional resinous reaction product is dispersed in deionized
water using a base such as a primary, secondary, and tertiary
alkyl, alkanol, or aromatic amine or alkanolalkyl mixed amine; e.g.
mono-ethanol amine, dimethyl ethanol amine, diethanol amine,
triethyl amine, dimethyl aniline, ammonium hydroxide, or the like.
Ordinarily this is done by adding the amine to some water, and the
mixing the resinous reaction product with the water.
The ease with which the dispersion will form will depend upon the
number of ionized sites and the strength and degree of ionization.
In some cases, agitation may be required to establish the
dispersion, although preferably, the strength and degree of
ionization will suffice so that a dispersion is easily established
and maintained.
For water reducible protective and decorative coating compositions
for general applications, there is great flexibility in
formulation. Some representative compositions are described below
in Table 2, in which the composition of the grafting base solids is
not specified, but may be as described above.
TABLE 3 ______________________________________ Step Three Products:
Representative Dispersion Compositions Component Parts by Weight
______________________________________ grafting base 95 75 60 37.5
12.5 addition polymerizable monomer including an acrylic acid 5 25
40 62.5 87.5 2-butoxy-ethanol-1 30.4 24 24 24 24 n-butanol 45.6 36
36 36 36 dimethyl ethanol amine (ionizing agent) 7.6 6 6 6 6
demineralized water 310 245 245 245 245 Total 493.6 411 411 411 411
______________________________________
The Table 2 compositions describe dispersions of neutralized,
ionized, acid-functional graft polymer resinous reaction products.
Base-functional resinous reaction products can be made in similar
fashion, by substituting an unsaturated amine for the unsaturated
acid in the monomer, during the grafting step, and by using an acid
or a quaternizing agent, or a mixture of these, for ionization.
To make a dispersion useful in the preparation of a sprayable can
coating composition from a Step 4 product, the film-forming
resinous solids should be derived from an initial reactant epoxy
PG,39 resin in an amount of at least about 50% by weight of the
solids, and preferably about 60%, and the epoxy resin should have
an EEW of at least 2,000. In terms of the grafting base, the
grafting base could contain, for example, at least about 60% by
weight of solids derived from or contributed by the epoxy resin
based on total solids; the epoxy resin should have an EEW of at
least 2,000 (and a molecular weight of at least 4,000); and the
grafting base should contribute at least about 78% by weight of the
solids present in the final product.
For example, if the can coating is to be based on at least 40%
epoxy, which is considered the minimum level for producing
acceptable properties, then if the grafting base is to contribute
80% of the solids of the coating, it must initially contain 50% by
weight of epoxy resin. Similarly, if the can coating is to be based
on at least 45% epoxy, a more preferred level, then the grafting
base must initially contain about 56% by weight of epoxy resin.
STEP FIVE
Vinyl Polymerization In Situ
Additional monomer is added to the dispersion produced by the
previous steps, together with additional initiator, and the
temperature is then raised to a suitable reaction temperature while
the mixture is agitated, to cause in situ polymerization of the
added monomer to occur. Generally more deionized water is also
added.
Since the end product of this step is an aqueous dispersion
containing added solids, the extent and degree or strength of
ionization already present in the dispersion will be important
factors in determining both the amount and the identity of the
monomer component employed in this fifth step. Thus, if sufficient
ionization is present to establish and maintain dispersed the
solids to be added, then there need not be additional ionizable
sites added, and the monomer component may be a material such as
styrene, selected for the properties that it will impart and for
its economy. On the other hand, if additional ionizable sites must
be introduced, then the monomer component will be selected
accordingly.
Additional demineralized water may also be added, so that the
material has the requisite characteristics for the kind of
application intended. For example, for spraying, a solids content
of about 19%-22% by weight is a preferred useful range to employ,
although the broader solids concentration of from 10% to 30% by
weight is useful. For application techniques other than spraying, a
solids content in the range from about 10% to about 40% or even
more is useful. While the use of an aminoplast cross-linker is
convenient, the products produced by the present invention are
self-cross-linking with heat to a limited extent, if terminal epoxy
groups are present.
The dispersions that are produced in accordance with the present
invention are generally useful as film-forming, surface coating
materials, the preferred application being in the formulation of
sprayable compositions for coating beverage cans.
The chemical system present in the dispersion products of the
present invention is a rather complicated one. Indications are that
after the in situ vinyl polymerization of step five, some
additional grafting may occur, when the initiator is one that
abstracts hydrogen. Complete, accurate characterization of the
solids present will require a good deal of work, due to the
complexity of the processes and the ingredients.
There are many advantages to modifying the dispersed reaction
product of the fourth step by supplementing its solids content
through the in situ vinyl polymerization. One obvious advantage is
economy, since generally, the material that is added is less
expensive than the epoxy component. In addition, the amount of
organic solvent as a percentage of the final product is
substantially reduced, through the addition of more solids and more
water. Another important advantage is that the in situ
polymerization can be carried out in the same reaction vessel in
which the graft polymer-containing resinous reaction product is
produced, and therefore does not require additional equipment, and
in fact, makes more efficient use of existing equipment.
Based upon 100 parts of resinous reaction product solids as input
for the in situ polymerization, about 10 parts to 225 parts of
added vinyl monomer represents a feasible range of addition.
However, a greater amount may be added if desired, if appropriate
steps are taken to compensate for the changed characteristics of
the product, having in mind the intended end use. On the other
hand, there is little point in going through this step unless a
significant amount of monomer is added to the solids already
present. While a practical minimum is about 10 parts of added
monomer for each 100 parts of input solids, as little can be added
as desired. One presently preferred practical range of addition is
from about 12 parts to about 70 parts added per 100 parts of input
resinous reaction product solids, for most coating
compositions.
In practice, a sufficient amount of monomer is added so that the
solids added contribute from about 10% to about 40% and preferably,
about one-third of the total solids in the final product. This can
often offer a material advantage in respect of economic
considerations without substantial loss in functional properties,
for example for sanitary (can) coatings produced in accordance with
one preferred embodiment of the invention, as hereafter
described.
For can coatings the amount of solids added at this stage will tend
to be governed by a balance of properties against cost. For good
properties, the epoxy resin should contribute at least 30% of total
solids, preferably 40%, and more preferably, about 45% to 50%, and
this factor, together with the amount and nature of other solids
already present, governs what and how much can be added in this
step.
In a variation, the resinous reaction product containing the graft
polymers may be prepared utilizing an amine, so that the graft
polymers and, depending on the process employed, the ungrafted
addition polymer also, may be base-functional. In this case,
dispersion in water is accomplished by the addition of an agent
that ionizes the amine groups. The resulting dispersion is then
useful for the in situ vinyl polymerization step, and in this case,
the added monomer should produce either nonionic products or
base-functional products.
Useful vinyl monomers for this step include vinylidene chloride;
arylalkenes, such as styrene, vinyl toluene, alpha-methyl styrene,
dichlorostyrene, and the like; C-1 to C-15 alkyl acrylate esters,
and particularly, lower alkyl acrylates, such as methyl acrylate,
butyl acrylate, and lower alkyl methacrylates, such as methyl
methacrylate, butyl methacrylate, and, as well, the nonyl, decyl,
lauryl, isobornyl, 2-ethyl hexyl, and octyl esters of acrylic or
methacrylic acid, also trimethylol-propane trimethacrylate,
1,6-hexanediol dimethacrylate, and the like; hydroxy lower alkyl
acrylates, such as hydroxy propyl acrylate, hydroxy ethyl acrylate,
and the like; hydroxy lower alkyl methacrylates, such as hydroxy
ethyl methacrylate, hydroxy propyl methacrylate, and the like;
lower alkenyl carboxylic acids, such as acrylic acid, methacrylic
acid, and the like; lower alkenyl amides, such as acrylamide,
methacrylamide, isobutoxymethylacrylamide, and the like; lower
hydroxyalkyl alkenyl amides such as hydroxy methyl acrylamide, and
the like; lower alkyl butenedioates such as dibutyl maleate,
dibutyl fumarate, and the like; vinyl lower alkenoates, such as
vinyl acetate, and vinyl propionate, and the like; and mixtures of
these.
Presently preferred vinyl monomers include styrene, butyl or ethyl
acrylate, and methacrylic acid, admixed, with a very small
proportion present of the acrylate ester. Up to about 25% allyl
materials by weight of total vinyl monomer may be included.
In order to cause the vinyl monomer to polymerize, at least one
initiator is introdued into the aqueous dispersion before or during
addition thereto, with agitation, of the vinyl monomer. As used
herein, the term "initiator" or "free radical initiator" has
reference to any substance which when added appears to promote
addition polymerization. The amount of initiator used typically is
in the range from about 0.1 to 5 parts per 100 parts by weight of
total vinyl monomer added, and preferably from about 0.5 to 3 parts
per 100 parts total vinyl monomer, but larger or smaller amounts
may be used.
Initiation provided by a redox system is extremely effective. An
organic peroxide may be used or an inorganic peroxide such as
hydrogen peroxide, ammonium persulfate, sodium persulfate, or
potassium persulfate. The peroxide catalyst is effectively coupled
with a reducing agent such as an alkali metal sulfite, bisulfite,
or metabisulfite, or hydrosulfite, or hydrazine. The action of the
redox system may be controlled through the use of a chain transfer
agent or regulator, such as mercaptoethanol or other mercaptan.
Such a regulator also finds use outside of redox systems with
organic or inorganic peroxides and with azo catalysts, such as
azodiisobutyronitrile, azodiisobutyramide, or diethyl
azodiisobutyrate. Examples of other suitable azo catalysts include
dimethyl or dibutyl azodiisobutyrate, azobis
(.alpha.,.gamma.-dimethylvaleronitrile), azobis
(.alpha.-methylbutyronitrile), azobis
(.alpha.-methylvaleronitrile), dimethyl or diethyl
azobismethylvalerate, and the like.
Preferred such initiators comprise the persulfates, such as
potassium persulfate, sodium persulfate, ammonium persulfate, and
the like. Another useful class of initiators comprises
percarbonates, such as diisopropyl percarbonate, and the like.
Another useful but less preferred class of initiators for this in
situ polymerization comprises organic peroxides. One group of
suitable peroxides comprises diacyl peroxides, such as benzoyl
peroxide, lauroyl peroxide, acetyl peroxide, caproyl peroxide,
butyl perbenzoate, 2,4-dichloro benzoyl peroxide, p-chlorobenzoyl
peroxide, and the like. Another group comprises ketone peroxides,
such as methyl ethyl ketone peroxide and the like. Another group
comprises alkyl hydroperoxides such as t-butyl hydroperoxide, and
the like. Another group comprises aqueous hydrogen peroxides.
Generally, the initiator is chosen with a half life such that an
effective amount is present during the polymerization to insure
complete reaction. The preferred initiators and those which are
virtually completely consumed when the polymerization is
complete.
Certain other classes of materials can be present at the time of,
or during such a polymerization, such as chain transfer agents such
as n-octylmercaptan, and t-dodecyl mercaptan; reducing agents, such
as sodium bisulfite, sodium formaldehyde sulfoxylate, sodium
hydrosulfite, and sodium thiosulfate, and the like agents. The
amount of such agents or additives if such as used is
characteristically less than about five weight percent based on
total solids present in a reaction system. Such additives are known
to those skilled in the art of vinyl monomer polymerization.
In general, in situ polymerization of the vinyl monomer in
accordance with the teachings of this invention permits wide
flexibility as to the kinds of initiator employed and the reaction
temperature. It generally proceeds under liquid phase conditions at
temperatures in the range from about 25.degree. C. to 100.degree.
C., and preferably from 50.degree. to 100.degree. C., and most
preferably, from about 50.degree. C. to 80.degree. C. When the
extender polymer employed exhibits a tendency to gel, those higher
temperatures that might favor gelation should be avoided.
Under some circumstances, the use of exceptionally high
temperatures may be desired. In such cases, when the epoxy resin
has been terminated to reduce the liklihood of desired reactions,
the polymerization temperature may be as high as 160.degree. C. The
rate of monomer polymerization is controlled not only by
temperature, but also by such variables as the amount and type of
initiator(s) used, initiator concentration, the concentration and
type of other solids present, and by other factors.
The vinyl monomer generally is added gradually or by increments to
an aqueous dispersion of the resinous reaction product at a rate
such that the exothermic polymerization can be controlled
adequately. Under favorable circumstances, such as controllable
exotherm, the monomer can be added in bulk, and this technique is
generally preferred for the production of dispersions to be used in
formulating sanitary coating compositions. However, some of the
monomer may be present with the dispersion as a "heel", at the time
the remainder of the monomer, plus initiator, is added.
The solids are already dispersed, and any further ionization
desired proceeds generally as in Step 4. Thus, for ionizing an in
situ acid-functional vinyl polymerizate (and any nonionized but
ionizable sites already present in the dispersion), dimethyl
ethanolamine is a preferred fugitive ionizing agent. Other fugitive
bases that may be employed include di-isopropanolamine,
triethanolamine, triisopropanolamine, diethyl ethanolamine, and
ammonia.
When the ionizable solids are base-functional, the neutralizing
agent employed is an acid, preferably a fugitive acid. A few
representative suitable materials are hydrochloric acid, sulfuric
acid, phosphoric acid, formic acid, chloroacetic acid, acetic acid,
glycolic acid, malic acid, maleic acid, fumaric acid, succinic
acid, lactic acid, and the like. Quaternizing agents may also be
employed in connection with tertiary amino nitrogens in the
molecule. These may include, for example, methyl iodide, dimethyl
sulfate, methyl chloride, ethyl chloride, and the like.
For coatings that will be in contact with edibles, toxic materials
should be avoided.
The product of this fifth step is a dispersion that contains a high
proportion of ionized, film-forming, polymeric material. The
ionized material consists of the ionized graft polymers, and the
ionized ungrafted addition polymer present. The solids in the
product are present as an ultrafine dispersion of very fine solid
particles in the aqueous vehicle, with the sizes of the particles
distributed over a broad range.
If in the third step, a grafting base containing 40 parts of epoxy
resin and 40 parts of polystyrene, in solution, is reacted with 20
parts of a monomer mixture consisting of a major amount of
methacrylic acid and minor amount of styrene, reacted at about
115.degree. C. to 120.degree. C. and in the presence of about 6.7%
BPO, dry basis, then an acid functional resinous reaction product
may be obtained that contains a substantial amount of graft
polymer, together with ungrafted, ionizable addition polymer, and
unreacted grafting base solids comprising unreacted epoxy resin and
unreacted extender polymer. If then, 15 to 50 parts of
ethylenically unsaturated monomer, such as styrene or styrene plus
methacrylic acid an/or ethyl acrylate, are subjected to addition
polymerization conditions in the presence of 75 parts by weight of
an aqueous dispersion at 22.5% N.V. of this acid functional
resinous reaction product, the added ethylenically unsaturated
monomer adds to the content of polymer solids present, while much
of the functionality of the original dispersion is preserved. The
dispersion that would be produced from such an in situ vinyl
polymerization would contain about 13.5 parts by weight of solids
derived from the grafting base solids, about 3.4 parts of solids
derived from the grafting step, and 15 to 50 parts of solids
derived from the in situ polymerized ethylenically unsaturated
monomer material. Such an aqueous dispersion would be useful in the
formulation of wood coatings, clear or pigmented, and could be
formulated for any type of application desired, i.e., brushing,
rolling, spraying, and the like.
Wide variations in composition are of course possible, for other
types of formulations intended for the same or other purposes. Some
of the possibilities are summarized briefly in the tabular
presentations in Tables 4 and 5 below. In Table 4, it is assumed
that 10 parts of solids are added by the in situ vinyl
polymerization step.
TABLE 4 ______________________________________ Representative
Product Compositions (By Weight, Dry Solids Basis), 10 Parts of
Solids Added In The in situ Vinyl Polymerization Component
Providing Source of Solids Parts % Parts % Parts % Parts %
______________________________________ Grafting 95 86.4 80 72.7 50
45.5 30 27.3 Third Step Addition Polymeri- zable Monomer 5 4.5 20
18.2 50 45.5 70 73.6 Fifth Step In Situ Vinyl Polymeriza- tion 10
9.1 10 9.1 10 9.1 10 9.1 Total 110 100 110 100 110 100 110 100
______________________________________
In Table 5, it is assumed that the added in situ polymerization
adds 40% by weight to the solids content of the dispersion.
TABLE 5 ______________________________________ Representative
Product Compositions (By Weight Dry, Solids Basis) 40% Solids Added
by the In Situ Vinyl Polymerization Component Providing Source of
Solids Parts % Parts % Parts % Parts %
______________________________________ Grafting Base 95 57 80 48 50
30 30 18 Third Step Addition Polymeriza- tion Monomer 5 3 20 12 50
30 70 42 Fifth Step In Situ Vinyl Polymeriza- tion 66 40 66 40 66
40 66 40 Total 166 100 166 100 166 100 166 100
______________________________________
In both tables above, the composition of the grafting base is not
specified. It may be selected and adjusted to produce desired final
product compositions and properties.
Those compositions having about 40% or more of total solids
contributed by the initial epoxy resin component wet and adhere to
metal surfaces well, and form good barrier films. The added
addition polymerizable monomer improves the weathering and other
characteristics of film formed from the composition. Where economy
is important, or for application to surfaces other than metal,
valuable coating compositions can be prepared with a relatively
small contribution from the epoxy resin.
For ease in handling, and for application properties, water may be
added during the in situ reaction, so that while the solids are
increased by this step in total amount, the solids concentration
may remain substantially constant. Obviously, changes in the
amount, proportions, or nature of the materials employed in this
step will affect the composition and properties of the final
product.
For general types of applications including spraying, the aqueous
dispersion may comprise, preferably, from about 10% to 40% solids,
which are proportioned as follows: about 0.1% to about 16% by
weight of a cross-linking agent, and about 6% to about 39.9% by
weight of the solids from a reaction mixture produced in accordance
with the present invention; and about 60% to about 90% volatile
components, generally divided into about 6% to about 35% organic
solvent, and about 25% to about 80% water. It is preferred but not
essential that some organic solvent be used to facilitate
application, and it is generally used in the ratio of one part by
weight of solvent to about three parts by weight of water.
The resulting aqueous coating composition can be applied
satisfactorily by any conventional method known in the coating
industry. Thus, spraying, rolling, dipping, flow coating or
electrodeposition applications can be used for both clear and
pigmented films. Often spraying is preferred. After application
onto a metal substrate, the coating is cured thermally at
temperatures in the range from about 95.degree. C. to about
235.degree. C. or higher, for periods in the range from about 1 to
about 20 minutes, such time being sufficient to effect curing as
well as volatilization of any fugitive component therein. Further,
films may be air dried at ambient temperatures for longer periods
of time.
If desired, some or even all of the organic solvent present can be
completely removed prior to final formulation, by vacuum
evaporation (distillation) at a moderate temperature. If this is
done, the solvent content of the final product may be as low as is
desired, including zero. This can be done for can coating
dispersions or for other applications if desired. If it is to be
done, the solvents selected for use in the process must have
boiling points below that of water.
SPRAYABLE COATING COMPOSITIONS
Since sprayable compositions are preferred and important
embodiments of the invention, they are treated separately in this
section.
The amount of water in the final product dispersion depends on the
viscosity desired, which, in turn, is related to the intended
method of application. For spraying, water amounting to about 60%
by weight of the dispersion represents a typical level, within a
preferred range of composition for the dispersion of from 10% to
30% by weight of solids and from about 70% to 90% of volatiles,
that is, fugitive base, water, and solvents. The fugitive base is
usually about from 2% to 6%, water from about 30% to 90% and the
organic solvents from about 5% to about 40%, all percentages being
by weight based on the sprayable dispersion. The solids comprise
about 9% to 29% of the reaction mixture solids, and about 1% to 10%
of a cross-linking agent, based on the sprayable dispersion.
The organic solvent can be made up of one or more of the known
solvents such as butanol (normal), 2-butoxy-ethanol-1, xylene,
toluene, and other solvents. It is preferred to use n-butanol in
combination with 2-butoxy-ethanol-1, in approximately equal
amounts. A representative OS/S ratio for a sprayable can coating is
about 0.5.
An aminoplast resin is preferred for use as the cross-linking
agent. It can be added before any final diluting, or thereafter.
Typical aminoplasts include melamine, benzoguanamine,
acetoguanamine, and urea resins such as urea formaldehyde.
Commercially available aminoplasts which are water soluble or water
dispersible and useful for the instant purpose includes Cymel 301,
Cymel 303, Cymel 370, and Cymel 373 (all being products of American
Cyanamid, Stamford, Conn., said aminoplasts being melamine based,
e.g., hexamethoxymethyl melamine for Cymel 301), and Beetle 80
aminoplasts (products of American Cyanamid which are methylated or
butylated ureas.)
Other suitable aminoplast resins are of the type produced by the
reaction of aldehyde and formoguanamine; ammeline;
2-chloro-4,6-diamine-1,3,5-triazine;
2-phenyl-p-oxy-4,6-diamino-1,3,5-triazine; and
2,4,6-triethyl-triamino-1,3,5-triazine. The mono-, di-, or triaryl
melamines, such as 2,4,6-triphenyltriamino-1,3,5-triazine, are
preferred. Other aldehydes used to react with the amino compound to
form the resinous material are crotonic aldehyde, acrolein, or
compounds which generate aldehydes, such as
hexamethylene-tetramine, paraldehyde, and the like.
If there is little or no oxirane functionality in the final
product, then a cross-linker is necessary; otherwise, it is
desirable but the product is self cross-linking to some extent with
heat.
Another way to introduce cross-linking capability into the reaction
mixture and the graft polymer is by utilizing as all or part of the
polymerizable monomer, in the initial reaction mixture, a material
such as acrylamide or an alkyl derivative thereof, or a material
such as bis maleimide.
The coating composition of the present invention can be pigmented
and/or opacified with known pigments and opacifiers. For many uses,
including food uses, the preferred pigment is titanium dioxide.
Often the pigment is used in a pigment-to-binder ratio of 0.1:1 to
1:1, by weight. Titanium dioxide pigment can be incorporated into
the composition in amounts in a preferred range of from about 5% to
40% by weight, based on resinous, film-forming solids in the
composition. Dyes may also be used, alone or in conjunction with
pigment.
For metal sheet substrates intended as beverage containers and
particularly for carbonated beverages such as beer, the coating
should be applied at a rate in the range from about 0.5 to about 15
milligrams of binder solids per square inch of exposed metal
surface. To attain the foregoing, the water-dispersible coating as
applied can be as thick as 1/10th mil. to about 1 mil.
Sprayable can coating compositions prepared in accordance with the
present invention are generally highly resistant to blistering and
are well suited for their intended purpose.
GENERAL
The properties of the fifth step product can be substantially
custom produced. The strength and degree of ionization in the
product can be such that the particles remain in stable suspension
almost indefinitely under room temperature storage conditions,
without agitation. The ionized material from the reaction product
of the third, grafting step appears to play a role in causing the
in situ polymerization to result in a product in which all of the
particles remain dispersed, whether they themselves are ionizable
or not.
It is possible to employ an external surfactant during the in situ
polymerization. The use of an external surfactant appears to be
possibly valuable for improving the coverage of coatings prepared
from the in situ polymerizate. A wide variety of commercially
available external surfactants is available for use. Anionic agents
such as Tamol 731 of Rohm and Haas and Daxad 30 of W. R. Grace are
exemplary. Other satisfactory external surfactants include Aerosol
MA, a product of American Cyanamid, available as an 80% solution in
water to tetra sodium
N-(1,2-dicarboxyethyl-N-octadecylsulfosuccinamate), and Aerosol 22,
another product of American Cyanamid, available as a 35% solution
in water of sodium dihexyl sulfosuccinate. Combinations of two or
more external surfactants may also be used.
The introduction of a wetting agent as an external surfactant may
affect blush resistance, particularly at baking temperatures below
375.degree. F. (191.degree. C.). The addition of a cross-linker
such as Cymel 303, however, apparently improves the situation.
The amount of solvent and water present in the fourth (dispersion)
step product should be kept at a level that facilitates handling.
Preferably, the solvent system used is a water-miscible system.
Epoxy resins are generally soluble in ketones, ethers, and esters.
Solvents that may be used are n-propyl ketone, methyl isobutyl
ketone, diisobutyl ether, n-propyl acetate, n-butyl acetate, ethyl
butyrate, an alkoxyethanol, or an alkyl ether of diethylene glycol.
The preferred solvent is 2-butoxy-ethanol-1.
Preferably, in addition to a solvent for the epoxy resin, a second
organic liquid solvent is present that need not necessarily
dissolve the epoxy resin itself, but that is preferably miscible
with the first solvent, and that preferably can dissolve or solvate
the side chains on the backbone resin in the graft polymer and the
addition polymer, that is associatively formed with the graft
polymer, in the third step as well. The preferred second solvent is
n-butanol.
One very important purpose of the solvent(s) is to facilitate
handling during the several process steps. The extender polymer
preferably is selected from solubility in the solvent system
used.
From the standpoints of ease of handling and workability, a 40%
concentration of solids in any product may be workable, depending
on its constitution, but a product at even 35% solids is very
thick. Accordingly, it will often be found convenient to produce
product at 20% to 30% solids content. The preferred dispersions are
opalescent in appearance.
The epoxy resins employed in the practice of the invention have
been identified primarily in terms of desired molecular weight
and/or EEW. They are more specifically identified in the earlier
applications mentioned above. Dow Chemical's D.E.R. 331 epoxy resin
is a preferred low molecular weight starting resin, but its EEW is
preferably advanced to about 4,000 or so for use. Comparable,
commercially available epoxy resins can be advanced to a useful EEW
with a catalyst such as sodium or potassium acetate or similar
alkaline material. Since some resins are sold in solvents and/or
with residual catalysts, care must be exercised.
Dow's D.E.R. 669 epoxy resin, EEW about 4,500, is useful, as is its
D.E.R. 668, EEW about 2,750. Shell's Epon Resin 1010, EEW about
5,000, and its Epon Resin 1009, EEW about 3,250, are also useful;
these are solid resins.
The invention will now be further explained by several
demonstrations of its practice. Throughout this application and
especially in the following examples, all parts and percentages are
by weight, and all temperatures are in .degree.C., unless expressly
stated to be otherwise. The epoxy resin molecular weights referred
to hereafter are those calculated from end group analysis data.
The first five examples describe the production of grafting
base.
GRAFTING BASE PRODUCTION
Example 1
Grafting Base: Epoxy Resin With Polystyrene
The polystyrene extender polymer was first formed as follows: 283
gms. of 2-butoxyethanol-1 was charged into a 5 liter round bottom
flask which was fitted with a water-cooled condenser, nitrogen
inlet, a stirrer, and a thermometer, heated by an electric heating
mantle. The 2-butoxyethanol-1 was heated to about 110.degree. C.
and to this heated solvent solution was gradually added a monomer
mixture composed of 74 gms. of styrene and 4 gms. of benzoyl
peroxide (BPO, 78% in H2O). The addition of monomer took 2 hours
then a short of chaser of 1.4 gms. of BPO (78%) in 10 gms. of
2-butoxyethanol-1 was added to the reaction mixture. After the
addition of the chaser, the addition mixture was held for 1/2 hour
and the chaser step was repeated. After the 2nd chaser was added,
the polymerization mixture was held for 2 hours. At the end of that
time a vacuum was applied to the reaction mixture to remove
water.
After the water was removed, 872 gms. of a liquid epoxy resin, Dow
DER-333, and 470 gms. of bisphenol A were charged into the reaction
flask. The temperature fell to 95.degree. C. and heating was
continued. When the temperature was at 140.degree. C., heating was
turned off and the exotherm raised the temperature to 151.degree.
C. At that time heating was resumed and the temperature reached
180.degree. C. in 5 minutes. The temperature was held at
170.degree. C. for the next 3 hours.
The oxirane value of the reaction mixture was determined at the end
of each hour during the 3 hour hold peroid. These oxirane values
were 0.3, 0.26, and 0.24, respectively. The method used for
determining oxirane value was that described in the issued patents
and published applications identified in the discussion above of
related patent applications. At the end of the 3 hour hold period,
254 gms. of 2-butoxyethanol-1 was added, followed by 889 gms. of
n-butanol.
The product was a solution of a fluent, filterable mixture of epoxy
resin with polystyrene, having the approximate composition of
Grafting Base 1-1 of Table 1A above. It is generally useful as a
material for grafting as in Step 3 of the process of this
invention, and as will be specifically described presently.
EXAMPLE 2
Grafting Base: Epoxy Resin With Polybutene
In this demonstration of grafting base production, the extender
polymer, polybutene, is a preformed, commercially available
polymer.
1141 gms. of a liquid epoxy resin, Dow DER-333, 614 gms. of
bisphenol A, 310 gms. of 2-butoxyethanol-1, and 435 gms. of
polybutene 24 (from Chevron Chemical Co., Calif.), were charged
into a 5 liter round bottom flask equipped with N.sub.2 inlet,
condenser, stirrer and a thermometer. The reaction mixture was
heated to 140.degree. C., where a small exotherm occurred. Heating
was resumed until the batch temperature increased to 175.degree. C.
The batch was then held at 175.degree. C. for 3 hours. The
viscosity of the resin was observed at the end of each hour hold,
measured in 2-butoxyethanol-1 at 40% NV, with the values R, S, and
S, respectively. At the end of the third hour hold, 996 gms. of
n-butanol were added to the reaction mixture, and the temperature
was then stabilized to 112.degree. C.
The product was a filterable solution of a mixture of epoxy resin
with polybutene, having approximately the composition of grafting
base 2-3 of Table 1A above. It also is generally useful as a
material for grafting, as in Step 3 of the process of this
invention.
EXAMPLE 3
Grafting Base: Epoxy Resin with Epoxidized Polybutadiene
Into a 5-liter round bottom flask equipped with nitrogen inlet,
water-cooled condenser, mechanical agitator and a thermometer was
charged 1085 gm. of liquid epoxy resin (Epon 828), 614 gm. of
bisphenol A, 57 gm. of xylene, 100 gm. of epoxidized polybutadiene
(Mn 700-800, oxirane oxygen content 7.5%), and 310 gm. of
2-butoxy-ethanol-1.
The reaction mixture was heated to 50.degree. C. under a nitrogen
sparge, and 0.5 gm. of sodium acetate trihydrate in 9 gm. of water
was added to the reaction mixture. At that time, the nitrogen was
turned off, a vacuum of 17" was applied and heating continued.
When the temperature reached 135.degree. C., the vacuum was turned
off and replaced by the nitrogen sparge. 25.5 gm. of liquid was
collected. There was an exotherm observed at
140.degree.-150.degree. C., and the temperature climbed to
180.degree. C., where it was maintained. After 3 hours at that
temperature, the viscosity of the batch was X- (the cut was made by
taking 10 gm. of the reaction mixture with 11.25 gm. of
2-butoxy-ethanol-1). At that time, heating was discontinued and
1200 gm. of n-butanol was carefully added.
The product was a fluent, filterable mixture of an
oxirane-terminated epoxy resin with epoxidized polybutadiene,
having the composition of Grafting Base 1-4 of Table 1A above. It
is generally useful as a material for grafting as in Step 3 of the
process of this invention, as will be described presently.
Generally, the extender polymer is one that is substantially inert
both to the epoxy resin and to the polyfunctional advancing agent,
under the conditions of advancement. However, as this example
demonstrates, it is feasible to use an extender polymer that is
merely of lesser reactivity to the advancing agent than is the
epoxy resin, and that is substantially non-reactive with the epoxy
resin itself under the conditions of advancement.
EXAMPLE 4
Grafting Base: Epoxy Resin with Coumarone-Indene Resin
Into a 5-liter round bottom flask was charged 1085 gm. of liquid
epoxy resin (Epon 828), 614 gm. of bisphenol A, 57 gm. of xylene,
300 gm. of coumaron-indene resin (Cumar-R-1 from Neville Chemical
Co., Mn 730) and 421 gm. of 2-butoxy-ethanol-1. The flask was
fitted with a water-cooled condenser, N2 inlet, mechanical stirrer
and a thermometer.
The mixture was heated under N2 sparge and at 80.degree. C., a
solution of 0.8 gm. of sodium acetate in 9 gm. of water was added
to the reaction mixture. At that time, a vacuum of 18 inches was
applied to the flask and heating continued. When the temperature
reached 140.degree. C., heating was stopped and the vacuum was
turned off. 33 gm. of liquid was collected in the vacuum trap.
There was a slight exotherm as the temperature increased to
150.degree. C., at which time heating was resumed. The temperature
was stabilized at 175.degree. C. for 4 hours. At the end of that
time, the viscosity of the reaction mixture was U (viscosity sample
prepared at 40% NV in 2-butoxy-ethanol-1). Heating was stopped and
1089 gm. of n-butanol was added.
The product was a fluent and filterable mixture of
oxirane-terminated epoxy resin with coumarone-indene resin, having
the composition of Grafting Base 1-5 of Table 1A above. It is
generally useful as a Step 3 grafting base.
EXAMPLE 5
Grafting Base: Epoxy Resin with Polybutadiene Resin
Into a 5-liter round bottom flask was charged 1085 gm. of liquid
epoxy resin (Epon 828), 614 gm. of bisphenol A, 57 gm. of xylene,
300 gm. of the polybutadiene and 421 gm. of 2-butoxy-ethanol-1. The
mixture was heated to 80.degree. C. under nitrogen sparge and 0.8
gm. of sodium acetate trihydrate in 9 gm. of water was added. A
vacuum of 20" was then applied to the reaction mixture and heating
continued.
At 140.degree. C., the vacuum was broken off and heating stopped.
41.5 gm. of liquid was collected in the vacuum trap. Heating was
continued, until the temperature reached 175.degree. C. At that
time the temperature was stabilized for 3 hours. At the end of that
time, the viscosity of the resin mixture was V(40% NV in
2-butoxy-ethanol-1). 1039 gm. of n-butanol was then added and
temperature was stabilized at 115.degree. C.
The product was a fluent and filterable mixture having the
composition of Grafting Base 6-1 of Table 3 above. It is generally
useful as a Step 3 grafting base.
THE GRAFTING AND DISPERSION STEPS
Example 6
Acid Functional Resinous Reaction Product From Grafting Base
1-1
The grafting base of Ex. 1 was utilized. A monomer mixture was made
up of:
______________________________________ Ingredient Grams
______________________________________ methacrylic acid 299 styrene
95 ethyl acrylate 4 benzoyl peroxide (moist; 78% active) 35
2-butoxyethanol-1 101 ______________________________________
This mixture was slowly added, over a two hour period, to the
grafting base, while maintaining the temperature at about
118.degree. C. 57 gms. of n-butanol was then added and the reaction
mixture was held at 110.degree. C. for 3 hours.
3,188 grams of the solution thus obtained, a graft
polymer-containing resinous reaction product (58.1% N.V., AN 85),
was added to a mixture of 3,862 grams of deionized (DI) water, 229
grams of 2-butoxyethanol-1, and 181 grams of dimethylethanol amine.
A dispersion formed with the following characteristics:
______________________________________ NV = 25.44% (30 min.
@400.degree. F.) Viscosity = 100 secs., #4 Ford cup at 25.degree.
AN (acid number) = 85.3 on NV BN (base number) = 62.8 on NV %
neutralization = 72% ______________________________________
This dispersion is useful in its own right. It can be formulated
with pigment and a cross-linker, to make a sprayable can coating
composition. It is also useful as a medium for in situ vinyl
polymerization, as will be described presently.
EXAMPLE 7
Acid Functional Resinous Reaction Product from Grafting Base
2-3
The temperature of the grafting base solution of Ex. 2 was adjusted
to about 112.degree. C. A monomer mixture of 283 gms. methacrylic
acid, 148 gms. styrene, 4 gms. of ethyl acrylate, 38.5 gms. benzoyl
peroxide (BPO 78% in water), and 111 gms. of 2-butoxyethanol-1 was
slowly added to the grafting base. The addition of this monomer
mixture took 2 hours. At the end of the monomer addition, 255 gms.
of n-butanol was added, and the reaction mixture was then held at
112.degree. C. for 3 hours. At the end of the 3 hour hold, the
graft polymer resinous reaction product was ready to be dispersed
in water. The resin viscosity was then K, as measured by dissolving
1 part of the resin solution in 1 part n-methyl pyrrolidone.
2,752 gms. of the graft polymer solution was slowly dropped into a
aqueous mixture composed of 3,971 gms. of deionized water and 135
gms. of dimethyl ethanolamine. The dispersion had much opalescent
color, an indication of rather small particle size. The constants
for the aqueous dispersion were:
______________________________________ NV = 24.4% AN = 73.3 BN =
50.1 Viscostiy = 22 secs. #4 Ford Cup Organic solvent/solids (OS/S)
= 0.77 ______________________________________
This dispersion product was also useful per se. When formulated
with an aminoplast it makes an excellent clear protective coating,
particularly useful for metal surfaces. It can be cured by air
drying but preferably is cured by baking.
EXAMPLE 8
Acid-Functional Resinous Reaction Product From Grafting Base
1-4
The temperature of the grafting base solution of Ex. 3 was adjusted
to 110.degree. C. A monomer mixture composed of the following was
then dropwise added:
______________________________________ methacrylic acid 283 gm.
styrene 148 gm. ethyl acrylate 4 gm. benzoyl peroxide (78% in
H.sub.2 O) 38.5 gm. n-butanol 111 gm.
______________________________________
The addition took 2 hours, and then 62 gm. of n-butanol was added.
The reaction mixture was then held for 3 hours.
At the end of that time, the Gardner viscosity of the reaction
mixture (1 pt. resin, 1 pt. N-methyl pyrrolidone) was I.
2705 gm. of the reaction mixture was slowly dropped into 3411 gm.
of deionized water and 152 gm. of dimethylethanolamine. The
temperature of the water was about 50.degree. C. At the end of the
drop, the temperature of the dispersion rose to 75.degree. C. 560
gm. of deionized water was then added to the dispersion.
The resulting dispersion had the following characteristics:
______________________________________ NV 24.2% OS/S 0.87
______________________________________
The ratio of epoxy:epoxidized polybutadiene:acrylic was
76:4.5:19.5.
EXAMPLE 9
Acid-Functional Resinous Reaction Product From Grafting Base
1-5
The temperature of the grafting base reaction mixture of Ex. 4 was
stabilized at 112.degree. C. A monomer mixture was prepared from
the following:
______________________________________ methacrylic acid 283 gm.
styrene 148 gm. ethyl acrylate 4 gm. benzoyl peroxide (78% in
H.sub.2 O) 38.5 gm. n-butanol 111 gm.
______________________________________
This mixture was added slowly to the grafting base over a period of
2 hours while keeping the temperature at least as high as
112.degree. C. After then adding 63 gm. of n-butanol, the reaction
mixture was held at 110.degree. C. for 3 hours.
A stainless steel vessel was then loaded with 3,411 gm. of
deionized (DI) water and 152 gm. of dimethyl ethanolamine. Then
2,711 gm. of the reaction mixture was slowly dropped into the
vessel, while mixing with a high lift mechanical agitator. A
dispersion formed easily. At the end of the drop, 560 gm. of
deionized water was added.
The constants for the dispersion are:
______________________________________ NV: 24.6% OS/S: 0.8
______________________________________
The ratio of epoxy: Cumar-R-1: acrylic was 70:12:18. The ratio of
butanol: 2-butoxy-ethanol-1 was 75:25.
EXAMPLE 10
Acid-Functional Resinous Reaction Product From Grafting Base
2-1
______________________________________ methacrylic acid 283 gm.
styrene 148 gm. ethyl acrylate 4 gm. benzoyl peroxide (78% in
water) 38.5 gm. n-butanol 111 gm.
______________________________________
While the grafting base 2-1 from Ex. 5 was maintained at about
115.degree. C., the monomer mix was slowly added over a 2 hour
period. At the end of the monomer addition, 63 gm. of n-butanol was
added and the reaction mixture was held for 3 hours at 112.degree.
C.
Into 3411 gm. of deionized water (50.degree. C.) and 152 gm. of
dimethylethanolamine, 2,777 gm. of the resin mixture was slowly
dropped. The dispersion formed easily and the constants of the
dispersion are similar to those of the previous example.
SUMMARY OF EXAMPLES 6-10
The dispersions of Exs. 6-10 are each useful per se, and can be
formulated with pigment solids, cross-linker, and other adjuvants
to make valuable coating compositions.
The resinous, film-forming solids in the dispersions of Examples 6
through 10 have the compositions tabulated in Table 6 below.
TABLE 6 ______________________________________ Step 4 Dispersion
Products: Composition of Solids Percentage by Weight Component Ex.
6 Ex. 7 Ex. 8 Ex. 9 Ex. 10 ______________________________________
Epoxy Resin 74 67 76 70 70 Extender polymer: Polystyrene 4 -- -- --
-- Polybutene -- 16.5 -- -- -- Epoxidized polybutadiene -- -- 4.5
-- -- Coumarone- indene -- -- -- 12 -- Polybutadiene -- -- -- -- 12
Acrylic 22 16.5 19.5 18 18
______________________________________
Each of these dispersions contains sufficient epoxy resin for
excellent adhesion to metal surfaces, and for the production of
films having good chemical inertness and hence good barrier
properties. Moreover, the balance of properties and the composition
of each is such as to permit the formulation of a sprayable
sanitary coating composition with excellent storage stability, good
application properties, and outstanding cured characteristics.
The amount of acrylic acid present is important since it imparts
acid functionality and hence ionizability. The respective amounts
of methacrylic acid (MAA) and of carboxyl group (COOH) are listed
in Table 7 below.
TABLE 7 ______________________________________ Step 4 Dispersion
Products: Methacrylic Acid and Carboxyl Components Percentage by
Weight of Total Resinous Solids Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10
______________________________________ MAA 16.5 10.7 12.7 11.7 11.7
Carboxyl 8.6 5.6 6.6 6.1 6.1
______________________________________
THE IN SITU POLYMERIZATION STEP
Example 11
Sprayable Can Coating Composition Epoxy: Polystyrene: Acrylic
The dispersion of Ex. 6 was used for this demonstration of in situ
vinyl (acrylic) polymerization for increasing the solids
content.
2400 gms. of the dispersion, 174 gms. of styrene, 26 gms. of
methacrylic acid, and 573 gms. of water were charged into a 5 liter
round bottom flask equipped with a stirrer, N.sub.2 inlet,
thermometer and a condenser. To this reaction mixture was added 1.1
gms. of sodium formaldehyde sulfoxylate in 10 gms. of DI water.
The reaction mixture was heated to 50.degree. C., and then 1.1 gms.
of t-butyl hydroperoxide (t-BHP) (90% in water) in 10 gms. of DI
water was added. The temperature was then raised to 80.degree. C.,
and at that temperature the reactants were held for 1 hours. At the
end of the 1 hour hold, 0.5 gms. of sodium formaldehyde sulfoxylate
in 5 gms. of DI H2O, and 0.5 gms. of t-BHP in 5 gms. of water were
added and held at 81.degree. C. for 1/2 hour. At that time another
shot of chaser (0.5 gms. of sodium formaldehyde sulfoxylate in 5
gms. of water and 0.5 gms. of t-BHP in of water) was added, and the
mixture was held for 11/2 hours at 81.degree. C. At the end of 1/2
hour, the non-volatiles were determined to be 24.06%. At the end of
11/2 hours, the non-volatiles were determined to be 24.17%. 783
gms. of DI water was then added.
The final constants for this material were:
______________________________________ NV = 19.25 (30 min.
400.degree. F.) Viscosity = 10 secs. #4 Ford dup An = 88.2 on NV BN
= 50.3 on NV % neutralization = 57%
______________________________________
The solids in this product are derived from the following sources,
the numbers representing proportions by weight:
______________________________________ epoxy resin 56 polystyrene
extender polymer 3 monomer: added during grafting 16 added during
in situ polymerization 25 Total Monomer 41 Total 100
______________________________________
In ratio form, the solids composition can be described as:
epoxy:polystyrene:acrylic=56:3:41.
This dispersion can be formulated with Cymel 303 aminoplast, up to
about 10% based on the dispersion, to form a sprayable, curable,
clear can coating. The coating can be opacified if desired, by the
addition of from about 1% to about 1.9% by weight of the dispersion
of pigment grade titanium dioxide.
EXAMPLE 12
Sprayable Protective Coating; Epoxy: Polybutene: Acrylic
The dispersion of Ex. 7 was used as the vehicle for this
demonstration of in situ polymerization for solids
agumentation.
2242 gms. of the dispersion, 800 gms. of DI water, 330 gms. of
styrene, and 50 gms. of methacrylic acid were charged into a 5
liter round bottom flask, and heated to 50.degree. C. 4 gms. of
sodium formaldehyde sulfoxylate in 40 gms. of DI water was then
added to the reaction mixture, followed by 4.4 gms. of t-butyl
hydroperoxide (t-BHP) (90% in water) in 40 gms. of DI water. The
reaction temperature was then raised to 75.degree. C. and held at
that temperature for 2 hours. At the end of the 2 hour hold, a
chaser composed of 2 gms. of sodium formaldehyde sulfoxylate in 20
gms. of water and 2.2 gms. of t-BHP in 20 gms. of water was added,
and the reaction mixture was held for 1 hour at 75.degree. C. At
the end of that time the chaser step was repeated. After another
hour on hold, 36 gms. of dimethyl ethanolamine and 32 gms. of water
were added and held for another hour at 75.degree. C. The constants
for the final material were:
______________________________________ NV = 25.1% AN = 79.5 BN =
51.4 Viscosity = 15 secs. #4 Ford cup OS/S = 0.48
Epoxy:polybutene:acrylic = 39:10:51
______________________________________
This dispersion can be formulated with pigment solids and a
cross-linker to form coating compositions that are useful for
general purpose protective and decorative coatings.
EXAMPLE 13
Sprayable Coating Composition: Epoxy: Epoxidized Polybutadiene:
Acrylic
The dispersion of Example 8 was used as the vehicle for this in
situ polymerization.
2260 gm of the dispersion and 1200 gm. of deionized water were
charged into a 5-liter round bottom flask equipped with a nitrogen
inlet, condenser, thermometer and mechanical agitator. The mixture
was heated to 50.degree. C. and a mixture of 330 gm. of styrene and
50 gm. of methacrylic acid was slowly added to the dispersion over
a period of 1 hour.
After the monomer addition, 4 gm. of sodium sulfoxylate
formaldehyde in 40 gm. of water, and 4.4 gm. of t-BHP (90% in
water) in 40 gm. of water, were added, and the temperature raised
to 71.degree. C. The temperature was held at 71.degree. C. for 2
hours, and a chaser of 2 gm. of sodium sulfoxylate formaldehyde in
20 gm. of water, and 2.2 gm. t-BHP in 20 gm. of water, was added.
The reaction was held another hour at 71.degree. C. At the end of
that time, the chaser step was repeated. 36 gm. of dimethyl
ethanolamine in 32 gm. of deionized water was then added and held
another hour. 100 gm. of n-butanol and 35 gm. of
dimethylethanolamine were added.
The resulting dispersion had the following constants:
______________________________________ NV 21.4% Viscosity 355 sec.
#4 Ford Cup AN 83.6 BN 88.6 % neutralization 105% OS/S 0.68
______________________________________
EXAMPLE 14
Coating Composition; Epoxy: Coumarone-Indene: Acrylic
The dispersion of Ex. 9 was augmented in solids content, and its
percentage of organic solvent reduced, by the following
operation.
2383 gm. of the dispersion from Ex. 9 and 1000 gm. of deionized
water were charged into a 5-liter round bottom flask. The mixture
was then heated to 50.degree. C. under agitation with a nitrogen
sparge. A monomer mix consisted of 330 gm. of styrene and 50 gm. of
methacrylic acid was added to the reaction mixture over an hour,
followed by 4 gm. of sodium sulfoxylate formaldehyde in 40 gm. of
water and 4.4 gm. of t-BHP (90% in water) in 40 gm. of water.
The temperature was raised to 76.degree. C., at which temperature,
the reaction mixture was held for 2 hours. At the end of the 2 hour
hold, a chaser of 2 gm. of the sodium sulfoxylate formaldehyde in
20 gm. of water and 2.2 gm. of t-BHP (90% in water) in 20 gm. of
water was added. The reaction was held for another hour at
76.degree. C. and the chaser step repeated. 36 gm. of
dimethylethanolamine and 32 gm. of deionized water were added and
the reaction mixture held for another hour.
The final dispersion has the following constants:
______________________________________ NV 21.6 Viscosity 14 secs.
(#4 Ford Cup) AN 88.7 BN 74.1 % neutralization 83.5 OS/S 0.54
______________________________________
The proportion of epoxy to coumarone-indene to acrylic were about
41:7:52. This dispersion was readily formulated into protective
coatings that were particularly useful for metal surfaces. It could
also be used directly for clear coatings, but more desirable
application and decorative properties were obtained by formulation
with added water and pigment solids, and preferably, an aminoplast
cross-linker.
EXAMPLE 15
Coating Composition: Epoxy: Polybutadiene: Acrylic
The dispersion of Ex. 10 was augmented in solids content, and its
percentage of organic solvent reduced, by the following in situ
vinyl polymerization.
To 2298 gm. of the dispersion of Ex. 10 was added 1200 gm. of
deionized water. The mixture was heated under N2 blanket to
50.degree. C. 330 gm. of styrene and 50 gm. of methacrylic acid
were slowly added to the dispersion over a period of an hour, and 4
gm. of sodium sulfoxylate formaldehyde in 40 gm. of water was added
followed by 4.4 gm. of t-BHP (90% in water) in 40 gm. of water. The
resultant reaction mixture was then heated to 75.degree. C. and
held for 2 hours at that temperature. At the end of the hold, a
chaser of 2 gm. of sodium sulfoxylate formaldehyde in 20 gm. of
water and 2.2 gm. of t-BHP (90% in water) in 20 gm. of water was
added, and reaction mixture was held for one hour. At the end of
that time, the chaser step was repeated. 36 gm. of
dimethylethanolamine and 32 gm. of water was then added and the
mixture held for another hour at 75.degree. C.
The dispersion had the following constants:
______________________________________ NV 23.2% Viscosity 27 secs.
(#4 Ford Cup) AN 80.4 BN 60.6 % neutralization 75.3 OS/S 0.5
Epoxy:acrylic:41:7:52 n-butanol/2-butoxy-ethanol-1 = 75/25
______________________________________
The dispersion was useful for the same purposes as the product of
Ex. 14.
SUMMARY OF EXAMPLES 11-15
The resinous, film-forming solids of the dispersions of Examples 11
through 15 have the compositions listed in Table 8 below.
TABLE 8 ______________________________________ Step 5 Dispersion
Products: Composition of Solids Percentage by Weight of Total
Resinous Solids Component Ex. 11 Ex. 12 Ex. 13 Ex. 14 Ex. 15
______________________________________ Epoxy Resin 56 39 44.8 41 41
Extender polymer: Polystyrene 3 -- -- -- -- Polybutene -- 10 -- --
-- Epoxidized Polybutadiene -- -- 2.7 -- -- Coumarone-Indene -- --
-- 7 -- Polybutadiene -- -- -- -- 7 Acrylic 41 51 52.5 52 52 Total
MAA (Approx.) 20 12 12.9 12.3 12.3 Total Carboxyl (Approx.) 10 6
6.7 6.4 6.4 ______________________________________
ALTERNATE PROCESS
Example 16
The Third Preferred Embodiment
Addition Of Extender Polymer Prior to the In Situ
Polymerization
A 100 gallon reactor was charged with the following:
263 lb. of Dow DER-331 liquid epoxy resin
13.8 lb. xylene
149 lbs. of bisphenol A
75 lbs. of 2-butoxyethanol-1
It should be noted that DER-331 resin is essentially the same as
the DER-333 resin used in the earlier examples, but lacks a
self-contained catalyst and xylene. The appropriate amount of
xylene is added above to make this resin have the same xylene
content as DER-333 resin.
The mixture was heated to 185.degree. F. and 55.8 gms. of sodium
acetate trihydrate in 39 gms. of DI H.sub.2 O was added to the
reaction mixture. The heating was resumed at a vacuum of 20 inches
was applied to the reactor. About 1/2 hour later, the temperature
reached 310.degree. F. At that time the vacuum was disconnected and
a nitrogen sparge was inserted. Six lbs. of volatiles were
collected at 320.degree. F. The temperature was held at 350.degree.
F. for 2 hours. At the end of that time the viscosity of the
reaction mixture was only V (40% NV in 2-butoxyethanol-1). Another
shot of catalyst, 28 gms. of sodium acetate trihydrate in 280 gms.
of DI water, was added below the surface. The reaction mixture was
then held at 350.degree. F. for another 4 hours. At the end of that
time, the viscosity of the advanced epoxy resin was Y (40% NV in
2-butoxyethanol-1).
At that time the reactor was sealed and 242 lbs. of n-butanol was
pumped into the reactor below the surface. The temperature of the
reactor was allowed to drop to 235.degree. F. (113.degree. C.).
After the n-butanol was added, a monomer mixture consisting of the
following:
69 lbs. of methacrylic acid
36 lbs. of styrene
439 gms. (0.97 lbs.) of ethyl acrylate
9.4 lbs. of BPO (78% NV in H.sub.2 O)
27 lbs. of 2-ethoxyethanol-1
was added over a period of 2 hours. Once the monomer mixture was
added, 15 lbs. of n-butanol was added into the reactor through the
monomer feed tank. The graft polymer resinous reaction product was
then held at 237.degree. F. (114.degree. C.) for 3 hours. At the
end of the hold, the viscosity was obtained as M-N (1 pt. resin in
1 pt. N-methylpyrrolidone).
The resinous reaction product was then dropped into a reducing
tank, over a period of about 1 hour. The reducing tank contained
1134 lb. of DI water, 64 lb. of n-butanol, and 50 lb. of dimethyl
ethanolamine. The reducing tank components were heated to about
150.degree. F. (65.degree. C.) before the drop. After the resinous
reaction product was dropped into the reducing tank, 160 lb. of DI
water was added. The constants for the dispersion were:
______________________________________ NV = 23.4% AN = 80.9 BN = 58
Viscosity - 72 secs. #4 Ford cup OS/S = 0.92
______________________________________
This dispersion was useful in its own right, in the formulation of
sprayable can coatings (see particularly related patent application
Ser. No. 788,611). However, for present purposes, it was used to
demonstrate a variant embodiment of the present invention.
Thus, 2420 gms. of this dispersion, 716 gms. of DI water, 18 gms.
of dimethyl ethanolamine, 165 gms. of styrene, 25 gms. of
methacrylic acid, and 190 gms. of polybutadiene (Lithene PL from
Revertex Corp. England), were charged into a 5 liter round bottom
flask equipped with agitator, N.sub.2 inlet, condenser and a
thermometer. The mixture was stirred for an hour and then heated to
55.degree. C., 4 gms. of sodium formaldehyde sulfoxylate in 40 gms.
of DI water, and 4.14 gms. t-BHP in 40 gms. of water were added.
The temperature was then raised to 75.degree. C. and held there for
2 hours. At the end of two hours, a chaser of 2 gms. of sodium
formaldehyde sulfoxylate in 20 gms. of water and 2.2 gms. of t-BHP
in 20 gms. of water was added to the reaction mixture and held for
1 hour at 75.degree. C. At the end of the hour hold, the chaser
step was repeated.
The constants for the final material were:
______________________________________ NV = 24.1% AN = 73.4 BN =
56.4 Viscosity = 15 secs. #4 Ford Cup Epoxy:polybutadiene:Acrylic =
47:20:33 ______________________________________
This material made an excellent spray coating and was particularly
well suited for formulation with cross-linkers and pigment.
This example was repeated twice with two different extender
polymers respectively. Considering the foregoing detailed
demonstration as producing a product dispersion 16A, a product 16B
was similarly made by substituting as the extender polymer
polybutene 24 from Chevron Chemical Co., and a product 16C was
similarly made by substituting as the extender polymer Cumar-R1, a
coumarone-indene resin from Neville Chemical Co.
The constants and compositions for these three products were
presented for comparison, as follows:
______________________________________ Product Properties 16A 16B
16C ______________________________________ % Non-Volatile 24.1 23.9
23.5 Viscosity (#4 Ford Cup at 25.degree. C.) 15 sec. 15 sec. 16
sec. Acid Number 73.4 73.8 75.7 Base Number 56.4 48.3 53.8 %
Neutralization 76.8 65.5 71.1 Ratio of n-butanol to
2-butoxyethanol-1 75/25 75/25 75/25 OS/S 0.55 0.55 0.55 Composition
Epoxy 47 47 47 Extender Polymer 20 20 20 Acrylic 33 33 33 Type of
Extender Polymer Poly- Polybutene Coumarone butadiene Indene
Copolymer ______________________________________
EXAMPLE 17
Coating Composition:Epoxy:Acrylic:Acrylic
Addition of Acrylic Extender Polymer Prior to the In Situ
Polymerization
In this demonstration of the third preferred embodiment of the
invention, an acrylic copolymer is used as the extender polymer,
and is formed in the presence of the earlier-formed graft polymer.
The initial step was that of advancing a liquid epoxy resin.
438 gms of a liquid epoxy resin (Epon 828), Shell Chemical Co., 248
gms of Bisphenol A, 23 gms of xylene and 125 gms of
2-butoxy-ethanol-1, were charged into a 5 liter round bottom flask
equipped with a N.sub.2 inlet, condenser, stirrer and a
thermometer. The reaction mixture was heated to 50.degree. C., then
a mixture of 0.32 g. of sodium acetate trihydrate and 3.6 gms of
water was added. When the temperature reached 120.degree. C., a
vacuum of 18" was applied to the reaction mixture and heating
continued.
At 140.degree. C. the heating was stopped and a small exotherm was
observed. The vacuum was broken off. 23 gms of liquid had collected
in the vacuum trap. Heating was continued until the temperature
reached 175.degree. C. At that time the temperature was stabilized
for 3 hours. At the end of that time, the viscosity of the resin
mixture was Z.sub.1 +1/2 (40% NV in 2-butoxyethanol-1). 484 gms of
n-butanol were then added slowly, and the temperature was then
stabilized at 110.degree. C.
For the grafting step, a monomer mixture was made up of:
______________________________________ Gms.
______________________________________ Methacrylic acid 114 Styrene
60 Ethyl acrylate 1.6 BPO 15.5 2-butoxyethanol-1 45
______________________________________
This mixture was slowly added over a two hour period to the resin
base while maintaining the temperature of the resin at 110.degree.
C. 25 gms of n-butanol were then added and the reaction mixture was
held at 110.degree. C. for 3 hours.
To add the extender polymer at this point, preparations were made
to form an acrylic copolymer in the presence of the graft polymer
prepared in the preceding reaction. To this end, a monomer mixture
was made up of:
______________________________________ Gms.
______________________________________ Styrene 1238 Methacrylic
acid 185.5 BPO 9.1 n-Butanol 436 2-butoxyethanol-1 172
______________________________________
This mixture was added over 21/2 hrs. to the graft
polymer-containing reaction mixture while the temperature was held
at 110.degree. C. After the addition was completed, 47 gms of
n-butanol was added and the reaction mixture was held another 2
hrs. at 110.degree. C. At the end of the 2 hr. hold period, a
chaser which contained 9.1 gms of BPO and 20 gms xylene was added,
and the reaction mixture was then held for another hour. The
mixture of acrylic copolymer-extender and of graft polymer resinous
reaction product was then ready to be dispersed in water. The resin
viscosity was M.sup.1/2 as measured by dissolving 1 part of the
resin solution in 1 part of N-methyl pyrrolidone.
Only a portion of the resin solution was dispersed in water. Thus,
2747 gms of the resin solution was slowly dropped into an aqueous
mixture composed of 3911 gms of deionized water and 152 gms of
dimethyl ethanolamine. The constants for the aqueous dispersion
were:
______________________________________ NV = 21.1% AN = 93.8 BN =
64.9 Viscosity = 3 min. #4 Ford Cup OS/S = 0.69
______________________________________
To carry out the in situ vinyl polymerization step, 2592 gms of the
above dispersion, 165 gms of styrene, and 25 gms of methacrylic
acid were charged into a 5 liter round bottom flask equipped with a
stirrer, N.sub.2 inlet, thermometer and a condenser. To this
reaction mixture 0.95 gms of sodium formaldehyde sulfoxylate in 20
gms of DI water was added.
The reaction mixture was heated to 50.degree. C. and then 2.1 gms
of t-butyl hydroperoxide (90% of water) in 20 gms of DI water was
added. The temperature was then raised to 80.degree. C. and at that
temperature the reaction mixture was held for 1 hour. At the end of
the 1 hour hold period, a chaser, which contained 0.19 gms of
sodium formaldehyde sulfoxylate in 10 gms of DI water and 0.21 gms
of t-BHP in 10 gms of water, was added, and the contents of the
flask were held at 80.degree. for additional 1 hour.
At the end of second hold period, a second chaser was added, and
held at 80.degree. for another hour. Then 18 gms of dimethyl
ethanolamine and 16 gms water were added, and the reaction mixture
was held for 1 more hour. Then the heat was turned off and the
reaction mixture was cooled to room temperature while stirring. The
final constants for this material were:
______________________________________ NV = 25.0% AN = 86.0 BN =
62.4 Visc. = 42 sec. #4 Ford Cup
______________________________________
This dispersion was useful as a sprayable, water-reducible coating
composition. The Acid Number is adequate to maintain the solids
dispersed over long storage periods, with substantially no settling
or change in viscosity or pH. This formulation is a particularly
remarkable achievement, since the contribution of the epoxy resin
to overall final solids content is below 25% by weight. The acrylic
extender provides the major contribution to the solids (in the
neighborhood of two-thirds by weight).
CONCLUSION
Compositions prepared in accordance with the present invention are
useful directly as coating compositions, or as the base from which
coating compositions can be formulated. However, in its preferred
embodiments, the invention is concerned with the formulation of
water-reducible, sprayable compositions that can be used for
coating cans for beverages, especially beer cans.
Such coatings prepared in accordance with the invention can be
formulated to offer economy, relatively low ratio of organic
solvents to solids (an important environmental consideration), and
the achievement of sprayable consistencies with the least organic
solvent content feasible. Moreover, such coatings can be formulated
to exhibit little discernible change in either viscosity or pH
after extended room temperature storage, indicating the absence of
gelation and the existence of "stable" dispersions (as that term is
used herein).
Beer can coating compositions prepared in accordance with preferred
embodiments of the present invention can be formulated to exhibit
good stability, turbidity resistance, blush properties, and
adhesion to cans, whether made of aluminum, steel, tin plate, or
other material. Such coating compositions can be formulated to cure
in a few seconds at 450.degree. F. or so (about 230.degree. C.),
and also at lower temperatures such as 350.degree. F. (177.degree.
C.), and to exhibit superior properties as to resin volatilization
(fuming). When filled, a properly coated can may be exposed to
elevated temperatures, as during pasteurization, without blush.
Properly coated cans prepared from preferred and appropriate
formulations impart little or no taste to the beverage, and the
beverage should not develop undesirable flavor notes, turbidity, or
haze.
In addition, the coatings can be formulated to permit the necessary
forming operations to be accomplished on the coated metal
substantially without the development of cracks, pin-holes, or the
like. Preferred coatings are resistant to pasteurization
temperatures and are substantially free of components that might
migrate into the beverage during pasteurization or storage.
While compositions prepared in accordance with the invention are
primarily intended for use as liquid coatings, they may be reduced
to powders for application or for reconstitution to flowable
form.
The process of the invention can make more efficient use of
manufacturing equipment per unit of solids sold, and thus can
reduce costs and the need for additional reactor capacity.
While the grafting and in situ polymerization steps have been
described and exemplified herein as each comprising a single
polymerization step, there may be two or even more successive such
polymerizations for each such step, depending upon the final
properties and composition desired.
Water dispersion sanitary coating compositions made in accordance
with preferred embodiments of this invention can be formulated to
perform well when sprayed by both air and airless devices, with
atomization being obtainable with any type of nozzle or pressure,
that is, spraying applications can be made at pressures in the
range from 2 psi up to 1,500 psi. These compositions generally have
excellent application properties, and generally their use is free
from problems with respect to blistering, sagging, solvent washing,
foaming, and excess flow.
Coating materials made in accordance with the invention can be
applied to tin plate, aluminum, and to metal coated with primers,
in a range of application thicknesses producing cured weights per
12-ounce can in the range from 1 to 10 mgs/in.sup.2, which is 50 to
300 mgs. per 12-ounce can. Film continuity generally is readily
attainable throughout this range.
While the invention has been disclosed by reference to the details
of preferred embodiments thereof, it is to be understood that such
disclosure is intended in an illustrative rather than in a limiting
sense, and it is contemplated that various modifications in the
compositions and processing techniques, in particular, will readily
occur to those skilled in the art, within the spirit of the
invention and within the scope of the appended claims.
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